diff --git a/packages/core/package.json b/packages/core/package.json
index ae758c9cf3..4544125bc4 100644
--- a/packages/core/package.json
+++ b/packages/core/package.json
@@ -35,6 +35,7 @@
     "@types/google-protobuf": "^3.7.2",
     "@types/jest": "^24.0.0",
     "@types/node": "^12.0.0",
+    "@types/react-helmet": "^5.0.15",
     "@types/react-sparklines": "^1.7.0"
   },
   "dependencies": {
diff --git a/packages/core/src/api/apis/definitions/alert.ts b/packages/core/src/api/apis/definitions/alert.ts
index f0d0bb3d72..133255c719 100644
--- a/packages/core/src/api/apis/definitions/alert.ts
+++ b/packages/core/src/api/apis/definitions/alert.ts
@@ -29,7 +29,7 @@ export type AlertApi = {
   /**
    * Post an alert for handling by the application.
    */
-  post(alert: AlertMessage);
+  post(alert: AlertMessage): void;
 };
 
 export const alertApiRef = new ApiRef<AlertApi>({
diff --git a/packages/core/src/api/apis/definitions/error.ts b/packages/core/src/api/apis/definitions/error.ts
index 01a6509715..f2a8509558 100644
--- a/packages/core/src/api/apis/definitions/error.ts
+++ b/packages/core/src/api/apis/definitions/error.ts
@@ -53,7 +53,7 @@ export type ErrorApi = {
   /**
    * Post an error for handling by the application.
    */
-  post(error: Error, context?: ErrorContext);
+  post(error: Error, context?: ErrorContext): void;
 };
 
 export const errorApiRef = new ApiRef<ErrorApi>({
diff --git a/packages/core/src/api/app/FeatureFlags.test.tsx b/packages/core/src/api/app/FeatureFlags.test.tsx
index cc09ebc61d..38fe457781 100644
--- a/packages/core/src/api/app/FeatureFlags.test.tsx
+++ b/packages/core/src/api/app/FeatureFlags.test.tsx
@@ -15,7 +15,10 @@
  */
 
 import { FeatureFlags as FeatureFlagsImpl } from './FeatureFlags';
-import { FeatureFlagState } from 'api/apis/definitions/featureFlags';
+import {
+  FeatureFlagState,
+  FeatureFlagsApi,
+} from 'api/apis/definitions/featureFlags';
 
 describe('FeatureFlags', () => {
   beforeEach(() => {
@@ -23,7 +26,7 @@ describe('FeatureFlags', () => {
   });
 
   describe('#getFlags', () => {
-    let featureFlags;
+    let featureFlags: FeatureFlagsApi;
 
     beforeEach(() => {
       featureFlags = new FeatureFlagsImpl();
@@ -121,7 +124,7 @@ describe('FeatureFlags', () => {
   });
 
   describe('#getRegisteredFlags', () => {
-    let featureFlags;
+    let featureFlags: FeatureFlagsApi;
 
     beforeEach(() => {
       featureFlags = new FeatureFlagsImpl();
@@ -146,7 +149,7 @@ describe('FeatureFlags', () => {
     });
 
     it('should get the correct values', () => {
-      const getByName = name =>
+      const getByName = (name: string) =>
         featureFlags.getRegisteredFlags().find(flag => flag.name === name);
 
       expect(getByName('registered-flag-0')).toBeUndefined();
diff --git a/packages/core/src/components/CopyTextButton/CopyTextButton.stories.tsx b/packages/core/src/components/CopyTextButton/CopyTextButton.stories.tsx
index 7fd78f8057..e8e1317e4e 100644
--- a/packages/core/src/components/CopyTextButton/CopyTextButton.stories.tsx
+++ b/packages/core/src/components/CopyTextButton/CopyTextButton.stories.tsx
@@ -16,13 +16,13 @@
 
 import React from 'react';
 import CopyTextButton from '.';
-import { ApiProvider, errorApiRef, ApiRegistry } from 'api';
+import { ApiProvider, errorApiRef, ApiRegistry, ErrorApi } from 'api';
 
 export default {
   title: 'CopyTextButton',
   component: CopyTextButton,
   decorators: [
-    storyFn => {
+    (storyFn: () => JSX.Element) => {
       // TODO: move this to common storybook config, requires core package to be separate from components
       const registry = ApiRegistry.from([
         [
@@ -32,7 +32,7 @@ export default {
               // eslint-disable-next-line no-alert
               window.alert(`Component posted error, ${error}`);
             },
-          },
+          } as ErrorApi,
         ],
       ]);
       return <ApiProvider apis={registry} children={storyFn()} />;
diff --git a/packages/core/src/components/CopyTextButton/CopyTextButton.test.tsx b/packages/core/src/components/CopyTextButton/CopyTextButton.test.tsx
index 2abf9d0622..28aaf2f0c0 100644
--- a/packages/core/src/components/CopyTextButton/CopyTextButton.test.tsx
+++ b/packages/core/src/components/CopyTextButton/CopyTextButton.test.tsx
@@ -18,7 +18,7 @@ import React from 'react';
 import { render } from '@testing-library/react';
 import { wrapInThemedTestApp } from '@backstage/test-utils';
 import CopyTextButton from './CopyTextButton';
-import { ApiRegistry, errorApiRef, ApiProvider } from 'api';
+import { ApiRegistry, errorApiRef, ApiProvider, ErrorApi } from 'api';
 
 jest.mock('popper.js', () => {
   const PopperJS = jest.requireActual('popper.js');
@@ -44,7 +44,7 @@ const apiRegistry = ApiRegistry.from([
       post(error) {
         throw error;
       },
-    },
+    } as ErrorApi,
   ],
 ]);
 
diff --git a/packages/core/src/components/CopyTextButton/CopyTextButton.tsx b/packages/core/src/components/CopyTextButton/CopyTextButton.tsx
index 86c3778d26..62295eb0ce 100644
--- a/packages/core/src/components/CopyTextButton/CopyTextButton.tsx
+++ b/packages/core/src/components/CopyTextButton/CopyTextButton.tsx
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-import React, { FC, useRef, useState } from 'react';
+import React, { FC, useRef, useState, MouseEventHandler } from 'react';
 import { IconButton, makeStyles, Tooltip } from '@material-ui/core';
 import PropTypes from 'prop-types';
 import CopyIcon from '@material-ui/icons/FileCopy';
@@ -66,7 +66,7 @@ const CopyTextButton: FC<Props> = props => {
   const inputRef = useRef<HTMLInputElement>(null);
   const [open, setOpen] = useState(false);
 
-  const handleCopyClick = e => {
+  const handleCopyClick: MouseEventHandler = e => {
     e.stopPropagation();
     setOpen(true);
 
diff --git a/packages/core/src/components/ProgressBars/CircleProgress.tsx b/packages/core/src/components/ProgressBars/CircleProgress.tsx
index b1f857d0ac..b2da573de3 100644
--- a/packages/core/src/components/ProgressBars/CircleProgress.tsx
+++ b/packages/core/src/components/ProgressBars/CircleProgress.tsx
@@ -55,7 +55,12 @@ const defaultProps = {
   max: 100,
 };
 
-export function getProgressColor(palette, value, inverse, max) {
+export function getProgressColor(
+  palette: BackstageTheme['palette'],
+  value: number,
+  inverse?: boolean,
+  max?: number,
+) {
   if (isNaN(value)) {
     return '#ddd';
   }
@@ -74,7 +79,7 @@ export function getProgressColor(palette, value, inverse, max) {
 
 const CircleProgress: FC<Props> = props => {
   const classes = useStyles(props);
-  const theme = useTheme();
+  const theme = useTheme<BackstageTheme>();
   const { value, fractional, inverse, unit, max } = {
     ...defaultProps,
     ...props,
diff --git a/packages/core/src/components/SortableTable/SortableTable.stories.tsx b/packages/core/src/components/SortableTable/SortableTable.stories.tsx
index 3938916156..2a903e1df7 100644
--- a/packages/core/src/components/SortableTable/SortableTable.stories.tsx
+++ b/packages/core/src/components/SortableTable/SortableTable.stories.tsx
@@ -33,7 +33,11 @@ const data = [
 const columns = [
   { id: 'id', label: 'ID' },
   { id: 'amount', disablePadding: false, numeric: true, label: 'AMOUNT' },
-  { id: 'status', label: 'STATUS', sortValue: row => row.statusValue },
+  {
+    id: 'status',
+    label: 'STATUS',
+    sortValue: (row: typeof data[0]) => row.statusValue,
+  },
 ];
 const footerData = [
   { id: 'total', amount: 4, statusValue: 2, status: <StatusError /> },
diff --git a/packages/core/src/components/StructuredMetadataTable/StructuredMetadataTable.stories.tsx b/packages/core/src/components/StructuredMetadataTable/StructuredMetadataTable.stories.tsx
index 5a04520dd1..334219c881 100644
--- a/packages/core/src/components/StructuredMetadataTable/StructuredMetadataTable.stories.tsx
+++ b/packages/core/src/components/StructuredMetadataTable/StructuredMetadataTable.stories.tsx
@@ -13,7 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-import React from 'react';
+import React, { FC } from 'react';
 import InfoCard from '../../layout/InfoCard';
 import { Grid } from '@material-ui/core';
 import StructuredMetadataTable from '.';
@@ -41,7 +41,7 @@ export default {
   component: StructuredMetadataTable,
 };
 
-const Wrapper = ({ children }) => (
+const Wrapper: FC<{}> = ({ children }) => (
   <Grid container spacing={4}>
     <Grid item>{children}</Grid>
   </Grid>
diff --git a/packages/core/src/components/SupportButton/SupportButton.tsx b/packages/core/src/components/SupportButton/SupportButton.tsx
index 076ec2d3c9..c884086bfa 100644
--- a/packages/core/src/components/SupportButton/SupportButton.tsx
+++ b/packages/core/src/components/SupportButton/SupportButton.tsx
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-import React, { FC, Fragment, useState } from 'react';
+import React, { FC, Fragment, useState, MouseEventHandler } from 'react';
 import {
   Button,
   Link,
@@ -58,10 +58,10 @@ const SupportButton: FC<Props> = ({
   // TODO: get plugin manifest with hook
 
   const [popoverOpen, setPopoverOpen] = useState(false);
-  const [anchorEl, setAnchorEl] = useState(null);
+  const [anchorEl, setAnchorEl] = useState<Element | null>(null);
   const classes = useStyles();
 
-  const onClickHandler = event => {
+  const onClickHandler: MouseEventHandler = event => {
     setAnchorEl(event.currentTarget);
     setPopoverOpen(true);
   };
diff --git a/packages/core/src/components/WarningPanel/WarningPanel.tsx b/packages/core/src/components/WarningPanel/WarningPanel.tsx
index 1d3b3e03db..a3e6ed6c78 100644
--- a/packages/core/src/components/WarningPanel/WarningPanel.tsx
+++ b/packages/core/src/components/WarningPanel/WarningPanel.tsx
@@ -15,17 +15,20 @@
  */
 
 import React, { FC } from 'react';
-import { Typography, withStyles, makeStyles } from '@material-ui/core';
+import { Typography, makeStyles } from '@material-ui/core';
 import { BackstageTheme } from '@backstage/theme';
 import ErrorOutline from '@material-ui/icons/ErrorOutline';
 
-const errorOutlineStyles = theme => ({
+const useErrorOutlineStyles = makeStyles<BackstageTheme>(theme => ({
   root: {
     marginRight: theme.spacing(1),
     fill: theme.palette.warningText,
   },
-});
-const ErrorOutlineStyled = withStyles(errorOutlineStyles)(ErrorOutline);
+}));
+const ErrorOutlineStyled = () => {
+  const classes = useErrorOutlineStyles();
+  return <ErrorOutline classes={classes} />;
+};
 
 const useStyles = makeStyles<BackstageTheme>(theme => ({
   message: {
diff --git a/packages/core/src/layout/ContentHeader/ContentHeader.test.tsx b/packages/core/src/layout/ContentHeader/ContentHeader.test.tsx
index 1ab171bcf1..6f5a1b24cc 100644
--- a/packages/core/src/layout/ContentHeader/ContentHeader.test.tsx
+++ b/packages/core/src/layout/ContentHeader/ContentHeader.test.tsx
@@ -20,7 +20,7 @@ import ContentHeader from './ContentHeader';
 import { wrapInThemedTestApp } from '@backstage/test-utils';
 
 jest.mock('react-helmet', () => {
-  return ({ defaultTitle }) => <div>defaultTitle: {defaultTitle}</div>;
+  return ({ defaultTitle }: any) => <div>defaultTitle: {defaultTitle}</div>;
 });
 
 describe('<ContentHeader/>', () => {
diff --git a/packages/core/src/layout/ErrorBoundary/ErrorBoundary.tsx b/packages/core/src/layout/ErrorBoundary/ErrorBoundary.tsx
index 9e9d639548..88ae99c3c9 100644
--- a/packages/core/src/layout/ErrorBoundary/ErrorBoundary.tsx
+++ b/packages/core/src/layout/ErrorBoundary/ErrorBoundary.tsx
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-import React, { ComponentClass, Component, SFC } from 'react';
+import React, { ComponentClass, Component, SFC, ErrorInfo } from 'react';
 
 type Props = {
   slackChannel?: string;
@@ -23,14 +23,14 @@ type Props = {
 
 type State = {
   error?: Error;
-  errorInfo?: string;
+  errorInfo?: ErrorInfo;
 };
 
 const ErrorBoundary: ComponentClass<
   Props,
   State
 > = class ErrorBoundary extends Component<Props, State> {
-  constructor(props) {
+  constructor(props: Props) {
     super(props);
 
     this.state = {
@@ -39,15 +39,10 @@ const ErrorBoundary: ComponentClass<
     };
   }
 
-  componentDidCatch(error, errorInfo) {
+  componentDidCatch(error: Error, errorInfo: ErrorInfo) {
     // eslint-disable-next-line no-console
     console.error(`ErrorBoundary, error: ${error}, info: ${errorInfo}`);
     this.setState({ error, errorInfo });
-
-    // Exposed for testing
-    if (this.props.onError) {
-      this.props.onError(error, errorInfo);
-    }
   }
 
   render() {
@@ -58,9 +53,7 @@ const ErrorBoundary: ComponentClass<
       return this.props.children;
     }
 
-    return (
-      <Error error={error} errorInfo={errorInfo} slackChannel={slackChannel} />
-    );
+    return <Error error={error} slackChannel={slackChannel} />;
   }
 };
 
@@ -68,7 +61,6 @@ export default ErrorBoundary;
 
 type EProps = {
   error?: Error;
-  errorInfo?: string;
   slackChannel?: string;
 };
 
diff --git a/packages/core/src/layout/Header/Header.test.tsx b/packages/core/src/layout/Header/Header.test.tsx
index 79d74791c8..85b15e33aa 100644
--- a/packages/core/src/layout/Header/Header.test.tsx
+++ b/packages/core/src/layout/Header/Header.test.tsx
@@ -20,7 +20,7 @@ import { wrapInThemedTestApp } from '@backstage/test-utils';
 import Header from './Header';
 
 jest.mock('react-helmet', () => {
-  return ({ defaultTitle }) => <div>defaultTitle: {defaultTitle}</div>;
+  return ({ defaultTitle }: any) => <div>defaultTitle: {defaultTitle}</div>;
 });
 
 describe('<Header/>', () => {
diff --git a/packages/core/src/layout/InfoCard/InfoCard.stories.tsx b/packages/core/src/layout/InfoCard/InfoCard.stories.tsx
index 611facd29c..e9fa831b40 100644
--- a/packages/core/src/layout/InfoCard/InfoCard.stories.tsx
+++ b/packages/core/src/layout/InfoCard/InfoCard.stories.tsx
@@ -13,7 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-import React from 'react';
+import React, { FC } from 'react';
 import InfoCard from '.';
 import { Grid } from '@material-ui/core';
 
@@ -25,7 +25,7 @@ export default {
   component: InfoCard,
 };
 
-const Wrapper = ({ children }) => (
+const Wrapper: FC<{}> = ({ children }) => (
   <Grid container spacing={4}>
     <Grid item>{children}</Grid>
   </Grid>
diff --git a/packages/core/src/layout/InfoCard/InfoCard.tsx b/packages/core/src/layout/InfoCard/InfoCard.tsx
index f3d03d29c8..d645b25aaa 100644
--- a/packages/core/src/layout/InfoCard/InfoCard.tsx
+++ b/packages/core/src/layout/InfoCard/InfoCard.tsx
@@ -163,10 +163,15 @@ const InfoCard: FC<Props> = ({
   if (variant) {
     const variants = variant.split(/[\s]+/g);
     variants.forEach(name => {
-      calculatedStyle = { ...calculatedStyle, ...VARIANT_STYLES.card[name] };
+      calculatedStyle = {
+        ...calculatedStyle,
+        ...VARIANT_STYLES.card[name as keyof typeof VARIANT_STYLES['card']],
+      };
       calculatedCardStyle = {
         ...calculatedCardStyle,
-        ...VARIANT_STYLES.cardContent[name],
+        ...VARIANT_STYLES.cardContent[
+          name as keyof typeof VARIANT_STYLES['cardContent']
+        ],
       };
     });
   }
diff --git a/packages/core/src/layout/TabbedCard/TabbedCard.stories.tsx b/packages/core/src/layout/TabbedCard/TabbedCard.stories.tsx
index cf9fa6e6c6..23c2ab5b49 100644
--- a/packages/core/src/layout/TabbedCard/TabbedCard.stories.tsx
+++ b/packages/core/src/layout/TabbedCard/TabbedCard.stories.tsx
@@ -23,7 +23,7 @@ export default {
   title: 'Tabbed Card',
   component: TabbedCard,
   decorators: [
-    storyFn => (
+    (storyFn: () => JSX.Element) => (
       <Grid container spacing={4}>
         <Grid item>{storyFn()}</Grid>
       </Grid>
@@ -72,9 +72,10 @@ export const WithFooterLink = () => {
 };
 
 export const WithControlledTabValue = () => {
-  const [selectedTab, setSelectedTab] = useState('one');
+  const [selectedTab, setSelectedTab] = useState<string | number>('one');
 
-  const handleChange = (_ev, newSelectedTab) => setSelectedTab(newSelectedTab);
+  const handleChange = (_ev: any, newSelectedTab: string | number) =>
+    setSelectedTab(newSelectedTab);
 
   return (
     <>
diff --git a/packages/core/src/layout/TabbedCard/TabbedCard.tsx b/packages/core/src/layout/TabbedCard/TabbedCard.tsx
index bd7443e924..4dd1399fb0 100644
--- a/packages/core/src/layout/TabbedCard/TabbedCard.tsx
+++ b/packages/core/src/layout/TabbedCard/TabbedCard.tsx
@@ -68,7 +68,7 @@ const TabbedCard: FC<Props> = ({
 
   const handleChange = onChange
     ? onChange
-    : (_ev, newSelectedIndex: number) => selectIndex(newSelectedIndex);
+    : (_ev: unknown, newSelectedIndex: number) => selectIndex(newSelectedIndex);
 
   let selectedTabContent: ReactNode;
   if (!value) {
diff --git a/packages/core/tsconfig.json b/packages/core/tsconfig.json
index 5c5c42c25f..7b73db2f0f 100644
--- a/packages/core/tsconfig.json
+++ b/packages/core/tsconfig.json
@@ -2,7 +2,6 @@
   "extends": "../../tsconfig.json",
   "include": ["src"],
   "compilerOptions": {
-    "baseUrl": "src",
-    "noImplicitAny": false
+    "baseUrl": "src"
   }
 }