diff --git a/src/constants.ts b/src/constants.ts
new file mode 100644
index 0000000..f61a2cc
--- /dev/null
+++ b/src/constants.ts
@@ -0,0 +1,19 @@
+import * as otypes from '@octokit/types'
+import {homedir} from 'os'
+import {join} from 'path'
+
+export const IS_MACOS = process.platform === 'darwin'
+export const IS_WINDOWS = process.platform === 'win32'
+
+export const VERSION_LATEST = 'latest'
+export const VERSION_NIGHTLY = 'nightly'
+export const VERSION_TRUNK = 'trunk'
+
+export const GRAALVM_BASE = join(homedir(), '.graalvm')
+export const GRAALVM_FILE_EXTENSION = IS_WINDOWS ? '.zip' : '.tar.gz'
+export const GRAALVM_GH_USER = 'graalvm'
+export const GRAALVM_PLATFORM = IS_WINDOWS ? 'windows' : process.platform
+export const JDK_HOME_SUFFIX = IS_MACOS ? '/Contents/Home' : ''
+
+export type LatestReleaseResponse =
+  otypes.Endpoints['GET /repos/{owner}/{repo}/releases/latest']['response']
diff --git a/src/graalvm-trunk.ts b/src/graalvm-trunk.ts
new file mode 100644
index 0000000..e5d7680
--- /dev/null
+++ b/src/graalvm-trunk.ts
@@ -0,0 +1,103 @@
+import * as c from './constants'
+import * as core from '@actions/core'
+import * as tc from '@actions/tool-cache'
+import {SpawnSyncOptionsWithStringEncoding, spawnSync} from 'child_process'
+import {mkdirP, mv} from '@actions/io'
+import {findJavaHomeInSubfolder} from './utils'
+import {join} from 'path'
+
+const GRAALVM_TRUNK_DL =
+  'https://github.com/oracle/graal/archive/refs/heads/master.zip'
+const GRAALVM_MX_DL =
+  'https://github.com/graalvm/mx/archive/refs/heads/master.zip'
+const DEFAULT_SUITES = '/compiler,/regex,/sdk,/tools,/truffle'
+const GRAAL_REPO_DIR = join(c.GRAALVM_BASE, 'graal')
+const VM_DIR = join(GRAAL_REPO_DIR, 'vm')
+const MX_DIR = join(c.GRAALVM_BASE, 'mx')
+const MX_EXEC = c.IS_WINDOWS ? 'mx.cmd' : 'mx'
+const SPAWN_OPTIONS: SpawnSyncOptionsWithStringEncoding = {
+  cwd: VM_DIR,
+  encoding: 'utf8',
+  stdio: 'inherit'
+}
+
+const COMPONENTS_TO_SUITE_NAME = new Map<string, string>([
+  ['espresso', '/espresso'],
+  ['js', '/graal-js'],
+  ['llvm-toolchain', '/sulong'],
+  ['native-image', '/substratevm'],
+  ['nodejs', '/graal-nodejs'],
+  ['python', 'graalpython'],
+  ['R', 'fastr'],
+  ['ruby', 'truffleruby'],
+  ['wasm', '/wasm']
+])
+
+export async function setUpGraalVMTrunk(
+  javaVersion: string,
+  components: string[]
+): Promise<string> {
+  const jdkId = `labsjdk-ce-${javaVersion}`
+
+  core.startGroup(`Downloading GraalVM sources, mx, and ${jdkId}...`)
+
+  await tc.extractZip(await tc.downloadTool(GRAALVM_TRUNK_DL), c.GRAALVM_BASE)
+  await mv(join(c.GRAALVM_BASE, 'graal-master'), GRAAL_REPO_DIR)
+
+  await tc.extractZip(await tc.downloadTool(GRAALVM_MX_DL), c.GRAALVM_BASE)
+  await mv(join(c.GRAALVM_BASE, 'mx-master'), MX_DIR)
+  core.addPath(MX_DIR)
+  core.debug(`"${MX_DIR}" added to $PATH`)
+
+  const labsJDKDir = join(c.GRAALVM_BASE, 'labsjdk')
+  await mkdirP(labsJDKDir)
+  spawnSync(
+    MX_EXEC,
+    ['--java-home=', 'fetch-jdk', '--jdk-id', jdkId, '--to', labsJDKDir],
+    SPAWN_OPTIONS
+  )
+  const labsJDKHome = findJavaHomeInSubfolder(labsJDKDir)
+  core.exportVariable('JAVA_HOME', labsJDKHome)
+  core.debug(`$JAVA_HOME set to "${labsJDKHome}"`)
+
+  core.endGroup()
+
+  const dynamicImports = toSuiteNames(components).join(',')
+  const mxArgs = [
+    '--no-download-progress', // avoid cluttering the build log
+    '--disable-installables=true', // installables not needed
+    '--force-bash-launchers=true', // disable native launchers
+    '--exclude-components=LibGraal', // avoid building libgraal to save time
+    '--dynamicimports',
+    dynamicImports
+  ]
+  if (core.isDebug()) {
+    spawnSync(MX_EXEC, mxArgs.concat('graalvm-show'), SPAWN_OPTIONS)
+  }
+  const graalvmHome = spawnSync(MX_EXEC, mxArgs.concat(['graalvm-home']), {
+    ...SPAWN_OPTIONS,
+    stdio: 'pipe'
+  })
+  core.startGroup('Building GraalVM CE from source...')
+  spawnSync(MX_EXEC, mxArgs.concat(['build']), SPAWN_OPTIONS)
+  core.endGroup()
+  const graalvmHomePath = graalvmHome.stdout.trim()
+  if (core.isDebug()) {
+    const cmd = c.IS_WINDOWS ? 'dir' : 'ls'
+    spawnSync(cmd, [graalvmHomePath], {stdio: 'inherit'})
+  }
+  return graalvmHomePath
+}
+
+function toSuiteNames(components: string[]): string[] {
+  const names = [DEFAULT_SUITES]
+  for (const component of components) {
+    const suiteName = COMPONENTS_TO_SUITE_NAME.get(component)
+    if (suiteName) {
+      names.push(suiteName)
+    } else {
+      throw new Error(`Unsupported component: ${component}`)
+    }
+  }
+  return names
+}
diff --git a/src/graalvm.ts b/src/graalvm.ts
new file mode 100644
index 0000000..38a3489
--- /dev/null
+++ b/src/graalvm.ts
@@ -0,0 +1,51 @@
+import * as c from './constants'
+import {downloadAndExtractJDK, getLatestRelease} from './utils'
+
+const GRAALVM_CE_DL_BASE =
+  'https://github.com/graalvm/graalvm-ce-builds/releases/download'
+const GRAALVM_REPO_NIGHTLY = 'graalvm-ce-dev-builds'
+const GRAALVM_REPO_RELEASES = 'graalvm-ce-builds'
+const GRAALVM_TAG_PREFIX = 'vm-'
+
+export async function setUpGraalVMLatest(javaVersion: string): Promise<string> {
+  const latestRelease = await getLatestRelease(GRAALVM_REPO_RELEASES)
+  const tag_name = latestRelease.tag_name
+  if (tag_name.startsWith(GRAALVM_TAG_PREFIX)) {
+    const latestVersion = tag_name.substring(
+      GRAALVM_TAG_PREFIX.length,
+      tag_name.length
+    )
+    return setUpGraalVMRelease(latestVersion, javaVersion)
+  }
+  throw new Error(`Could not find latest GraalVM release: ${tag_name}`)
+}
+
+export async function setUpGraalVMNightly(
+  javaVersion: string
+): Promise<string> {
+  const latestNightly = await getLatestRelease(GRAALVM_REPO_NIGHTLY)
+  const graalVMIdentifier = determineGraalVMIdentifier('dev', javaVersion)
+  const expectedFileName = `${graalVMIdentifier}${c.GRAALVM_FILE_EXTENSION}`
+  for (const asset of latestNightly.assets) {
+    if (asset.name === expectedFileName) {
+      return downloadAndExtractJDK(asset.browser_download_url)
+    }
+  }
+  throw new Error('Could not find GraalVM nightly build')
+}
+
+export async function setUpGraalVMRelease(
+  version: string,
+  javaVersion: string
+): Promise<string> {
+  const graalVMIdentifier = determineGraalVMIdentifier(version, javaVersion)
+  const downloadUrl = `${GRAALVM_CE_DL_BASE}/${GRAALVM_TAG_PREFIX}${version}/${graalVMIdentifier}${c.GRAALVM_FILE_EXTENSION}`
+  return downloadAndExtractJDK(downloadUrl)
+}
+
+function determineGraalVMIdentifier(
+  version: string,
+  javaVersion: string
+): string {
+  return `graalvm-ce-java${javaVersion}-${c.GRAALVM_PLATFORM}-amd64-${version}`
+}
diff --git a/src/main.ts b/src/main.ts
index efee84f..637a4bb 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -1,9 +1,48 @@
+import * as c from './constants'
 import * as core from '@actions/core'
+import * as graalvm from './graalvm'
+import {join} from 'path'
+import {mkdirP} from '@actions/io'
+import {setUpGraalVMTrunk} from './graalvm-trunk'
 
 async function run(): Promise<void> {
   try {
+    const graalvmVersion: string = core.getInput('version', {required: true})
+    const javaVersion: string = core.getInput('java-version', {required: true})
+    const componentsString: string = core.getInput('components')
+    const components: string[] =
+      componentsString.length > 0 ? componentsString.split(',') : []
+    const setJavaHome = core.getInput('set-java-home') === 'true'
+
+    await mkdirP(c.GRAALVM_BASE)
+
+    // Download or build GraalVM
     let graalVMHome
+    switch (graalvmVersion) {
+      case c.VERSION_LATEST:
+        graalVMHome = await graalvm.setUpGraalVMLatest(javaVersion)
+        break
+      case c.VERSION_NIGHTLY:
+        graalVMHome = await graalvm.setUpGraalVMNightly(javaVersion)
+        break
+      case c.VERSION_TRUNK:
+        graalVMHome = await setUpGraalVMTrunk(javaVersion, components)
+        break
+      default:
+        graalVMHome = await graalvm.setUpGraalVMRelease(
+          graalvmVersion,
+          javaVersion
+        )
+        break
+    }
+
+    // Activate GraalVM
+    core.debug(`Activating GraalVM located at '${graalVMHome}'...`)
     core.exportVariable('GRAALVM_HOME', graalVMHome)
+    core.addPath(join(graalVMHome, 'bin'))
+    if (setJavaHome) {
+      core.exportVariable('JAVA_HOME', graalVMHome)
+    }
   } catch (error) {
     if (error instanceof Error) core.setFailed(error.message)
   }
diff --git a/src/utils.ts b/src/utils.ts
new file mode 100644
index 0000000..d70df3b
--- /dev/null
+++ b/src/utils.ts
@@ -0,0 +1,55 @@
+import * as c from './constants'
+import * as core from '@actions/core'
+import * as httpClient from '@actions/http-client'
+import * as tc from '@actions/tool-cache'
+import {Octokit} from '@octokit/core'
+import {join} from 'path'
+import {readdirSync} from 'fs'
+
+// Set up Octokit in the same way as @actions/github (see https://git.io/Jy9YP)
+const baseUrl = process.env['GITHUB_API_URL'] || 'https://api.github.com'
+const GitHub = Octokit.defaults({
+  baseUrl,
+  request: {
+    agent: new httpClient.HttpClient().getAgent(baseUrl)
+  }
+})
+
+export async function getLatestRelease(
+  repo: string
+): Promise<c.LatestReleaseResponse['data']> {
+  const githubToken = core.getInput('github-token')
+  const options = githubToken.length > 0 ? {auth: githubToken} : {}
+  const octokit = new GitHub(options)
+  return (
+    await octokit.request('GET /repos/{owner}/{repo}/releases/latest', {
+      owner: c.GRAALVM_GH_USER,
+      repo
+    })
+  ).data
+}
+
+export async function downloadAndExtractJDK(
+  downloadUrl: string
+): Promise<string> {
+  const downloadPath = await tc.downloadTool(downloadUrl)
+  if (downloadUrl.endsWith('.tar.gz')) {
+    await tc.extractTar(downloadPath, c.GRAALVM_BASE)
+  } else if (downloadUrl.endsWith('.zip')) {
+    await tc.extractZip(downloadPath, c.GRAALVM_BASE)
+  } else {
+    throw new Error(`Unexpected filetype downloaded: ${downloadUrl}`)
+  }
+  return findJavaHomeInSubfolder(c.GRAALVM_BASE)
+}
+
+export function findJavaHomeInSubfolder(searchPath: string): string {
+  const baseContents = readdirSync(searchPath)
+  if (baseContents.length === 1) {
+    return join(searchPath, baseContents[0], c.JDK_HOME_SUFFIX)
+  } else {
+    throw new Error(
+      `Unexpected amount of directory items found: ${baseContents.length}`
+    )
+  }
+}