diff --git a/LICENSE.dependencies.txt b/LICENSE.dependencies.txt
index 240688b5..8441676e 100644
--- a/LICENSE.dependencies.txt
+++ b/LICENSE.dependencies.txt
@@ -12,7 +12,7 @@ license-checker --summary --production
 ```
 
 ```
-├─ MIT: 4
+├─ MIT: 5
 ├─ ISC: 1
 └─ Apache-2.0: 1
 ```
\ No newline at end of file
diff --git a/README.md b/README.md
index 731b78cc..d77fc60c 100644
--- a/README.md
+++ b/README.md
@@ -15,7 +15,7 @@ The package will be usable from any environment (locally, GitHub Actions, etc).
 
 - [x] setup cmake
 - [x] setup ninja
-- [ ] setup llvm
+- [x] setup llvm
 - [ ] setup gcc/mingw
 - [ ] setup msvc
 - [ ] setup conan
diff --git a/action.yml b/action.yml
index 150a8661..2dceee2e 100644
--- a/action.yml
+++ b/action.yml
@@ -3,12 +3,12 @@ description: "Install all the tools required for building and testing C++/C proj
 author: "Amin Yahyaabadi"
 
 inputs:
-  compiler:
-    description: "The compiler and its version."
-    required: false
   architecture:
     description: "The CPU architecture"
     required: false
+  llvm:
+    description: "The llvm version to install"
+    required: false
   cmake:
     description: "The cmake version to install."
     default: "3.20.2"
diff --git a/package.json b/package.json
index 23caccde..a4126aab 100644
--- a/package.json
+++ b/package.json
@@ -32,11 +32,12 @@
   },
   "prettier": "prettier-config-atomic",
   "dependencies": {
+    "@actions/exec": "^1.1.0",
     "@actions/core": "^1.5.0",
     "@actions/io": "^1.1.1",
     "@actions/tool-cache": "^1.7.1",
-    "semver": "^7.3.5",
-    "hasha": "^5.2.2"
+    "hasha": "^5.2.2",
+    "semver": "^7.3.5"
   },
   "devDependencies": {
     "@types/jest": "^27.0.1",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 77ecec8c..016a850b 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -5,6 +5,7 @@ importers:
   .:
     specifiers:
       '@actions/core': ^1.5.0
+      '@actions/exec': ^1.1.0
       '@actions/io': ^1.1.1
       '@actions/tool-cache': ^1.7.1
       '@types/jest': ^27.0.1
@@ -24,6 +25,7 @@ importers:
       typescript: ^4.4.3
     dependencies:
       '@actions/core': 1.5.0
+      '@actions/exec': 1.1.0
       '@actions/io': 1.1.1
       '@actions/tool-cache': 1.7.1
       hasha: 5.2.2
@@ -8112,6 +8114,7 @@ packages:
   /type-fest/0.8.1:
     resolution: {integrity: sha512-4dbzIzqvjtgiM5rw1k5rEHtBANKmdudhGyBEajN01fEyhaAIhsoKNy6y7+IN93IfpFtwY9iqi7kD+xwKhQsNJA==}
     engines: {node: '>=8'}
+    dev: false
 
   /typedarray-to-buffer/3.1.5:
     resolution: {integrity: sha512-zdu8XMNEDepKKR+XYOXAVPtWui0ly0NtohUscw+UmaHiAWT8hrV1rr//H6V+0DvJ3OQ19S979M0laLfX8rm82Q==}
diff --git a/src/llvm/__tests__/llvm.test.ts b/src/llvm/__tests__/llvm.test.ts
new file mode 100644
index 00000000..bc18dddf
--- /dev/null
+++ b/src/llvm/__tests__/llvm.test.ts
@@ -0,0 +1,31 @@
+import { getSpecificVersionAndUrl } from "../llvm"
+import * as https from "https"
+
+jest.setTimeout(100000)
+
+function testUrl(version: string) {
+  const [specificVersion, url] = getSpecificVersionAndUrl(process.platform, version)
+
+  const input = `Version: ${version} => ${specificVersion} \n URL: ${url}`
+
+  return new Promise<string>((resolve, reject) => {
+    https.get(url, (res) => {
+      const report = `${input}\nStatus: ${res.statusCode}\nContent-Length: ${res.headers["content-length"]}`
+      if (res.statusCode !== undefined && res.statusCode >= 200 && res.statusCode <= 399) {
+        resolve(report)
+      } else {
+        reject(new Error(`Failed to download LLVM and Clang binaries.\n${input}\n${report}`))
+      }
+    })
+  })
+}
+
+describe("setup-llvm", () => {
+  it("Finds valid LLVM URLs", async () => {
+    await Promise.all(
+      ["12.0.0", "12", "11", "11.0.0", "10", "10.0.0", "9.0.0", "8.0.0", "7.0.0", "6", "6.0.0", "5", "5.0.0", "4"].map(
+        (version) => testUrl(version)
+      )
+    )
+  })
+})
diff --git a/src/llvm/llvm.ts b/src/llvm/llvm.ts
new file mode 100644
index 00000000..f4e9a38a
--- /dev/null
+++ b/src/llvm/llvm.ts
@@ -0,0 +1,303 @@
+import * as core from "@actions/core"
+import * as exec from "@actions/exec"
+import * as io from "@actions/io"
+import * as tc from "@actions/tool-cache"
+import * as path from "path"
+import semverLte from "semver/functions/lte"
+
+//================================================
+// Version
+//================================================
+
+/**
+ * Gets the specific and minimum LLVM versions that can be used to refer to the supplied specific LLVM versions (e.g.,
+ * `3`, `3.5`, `3.5.2` for `3.5.2`).
+ */
+function getVersions(specific: string[]): Set<string> {
+  const versions = new Set(specific)
+
+  for (const version of specific) {
+    versions.add(/^\d+/.exec(version)![0])
+    versions.add(/^\d+\.\d+/.exec(version)![0])
+  }
+
+  return versions
+}
+
+/** The specific and minimum LLVM versions supported by this action. */
+const VERSIONS: Set<string> = getVersions([
+  "3.5.0",
+  "3.5.1",
+  "3.5.2",
+  "3.6.0",
+  "3.6.1",
+  "3.6.2",
+  "3.7.0",
+  "3.7.1",
+  "3.8.0",
+  "3.8.1",
+  "3.9.0",
+  "3.9.1",
+  "4.0.0",
+  "4.0.1",
+  "5.0.0",
+  "5.0.1",
+  "5.0.2",
+  "6.0.0",
+  "6.0.1",
+  "7.0.0",
+  "7.0.1",
+  "7.1.0",
+  "8.0.0",
+  "8.0.1",
+  "9.0.0",
+  "9.0.1",
+  "10.0.0",
+  "10.0.1",
+  "11.0.0",
+  "11.0.1",
+  "11.1.0",
+  "12.0.0",
+  "12.0.1",
+])
+
+/**
+ * Gets the specific LLVM versions supported by this action compatible with the supplied (specific or minimum) LLVM
+ * version in descending order of release (e.g., `5.0.2`, `5.0.1`, and `5.0.0` for `5`).
+ */
+function getSpecificVersions(version: string): string[] {
+  return Array.from(VERSIONS)
+    .filter((v) => /^\d+\.\d+\.\d+$/.test(v) && v.startsWith(version))
+    .sort()
+    .reverse()
+}
+
+//================================================
+// URL
+//================================================
+
+/** Gets a LLVM download URL for GitHub. */
+function getGitHubUrl(version: string, prefix: string, suffix: string): string {
+  const file = `${prefix}${version}${suffix}`
+  return `https://github.com/llvm/llvm-project/releases/download/llvmorg-${version}/${file}`
+}
+
+/** Gets a LLVM download URL for https://releases.llvm.org. */
+function getReleaseUrl(version: string, prefix: string, suffix: string): string {
+  const file = `${prefix}${version}${suffix}`
+  return `https://releases.llvm.org/${version}/${file}`
+}
+
+/** The LLVM versions that were never released for the Darwin platform. */
+const DARWIN_MISSING: Set<string> = new Set([
+  "3.5.1",
+  "3.6.1",
+  "3.6.2",
+  "3.7.1",
+  "3.8.1",
+  "3.9.1",
+  "6.0.1",
+  "7.0.1",
+  "7.1.0",
+  "8.0.1",
+  "11.0.1",
+  "11.1.0",
+  "12.0.1",
+])
+
+/** Gets an LLVM download URL for the Darwin platform. */
+function getDarwinUrl(version: string): string | null {
+  if (DARWIN_MISSING.has(version)) {
+    return null
+  }
+
+  const darwin = version === "9.0.0" ? "-darwin-apple" : "-apple-darwin"
+  const prefix = "clang+llvm-"
+  const suffix = `-x86_64${darwin}.tar.xz`
+  if (semverLte(version, "9.0.1")) {
+    return getReleaseUrl(version, prefix, suffix)
+  } else {
+    return getGitHubUrl(version, prefix, suffix)
+  }
+}
+
+/**
+ * The LLVM versions that should use the last RC version instead of the release version for the Linux (Ubuntu) platform.
+ * This is useful when there were binaries released for the Linux (Ubuntu) platform for the last RC version but not for
+ * the actual release version.
+ */
+const UBUNTU_RC: Map<string, string> = new Map([["12.0.1", "12.0.1-rc4"]])
+
+/** The (latest) Ubuntu versions for each LLVM version. */
+const UBUNTU: { [key: string]: string } = {
+  "3.5.0": "-ubuntu-14.04",
+  "3.5.1": "",
+  "3.5.2": "-ubuntu-14.04",
+  "3.6.0": "-ubuntu-14.04",
+  "3.6.1": "-ubuntu-14.04",
+  "3.6.2": "-ubuntu-14.04",
+  "3.7.0": "-ubuntu-14.04",
+  "3.7.1": "-ubuntu-14.04",
+  "3.8.0": "-ubuntu-16.04",
+  "3.8.1": "-ubuntu-16.04",
+  "3.9.0": "-ubuntu-16.04",
+  "3.9.1": "-ubuntu-16.04",
+  "4.0.0": "-ubuntu-16.04",
+  "5.0.0": "-ubuntu16.04",
+  "5.0.1": "-ubuntu-16.04",
+  "5.0.2": "-ubuntu-16.04",
+  "6.0.0": "-ubuntu-16.04",
+  "6.0.1": "-ubuntu-16.04",
+  "7.0.0": "-ubuntu-16.04",
+  "7.0.1": "-ubuntu-18.04",
+  "7.1.0": "-ubuntu-14.04",
+  "8.0.0": "-ubuntu-18.04",
+  "9.0.0": "-ubuntu-18.04",
+  "9.0.1": "-ubuntu-16.04",
+  "10.0.0": "-ubuntu-18.04",
+  "10.0.1": "-ubuntu-16.04",
+  "11.0.0": "-ubuntu-20.04",
+  "11.0.1": "-ubuntu-16.04",
+  "11.1.0": "-ubuntu-16.04",
+  "12.0.0": "-ubuntu-20.04",
+  "12.0.1-rc4": "-ubuntu-21.04",
+}
+
+/** The latest supported LLVM version for the Linux (Ubuntu) platform. */
+const MAX_UBUNTU: string = "12.0.1-rc4"
+
+/** Gets an LLVM download URL for the Linux (Ubuntu) platform. */
+function getLinuxUrl(versionGiven: string): string {
+  let version = versionGiven
+
+  const rc = UBUNTU_RC.get(version)
+  if (rc !== undefined) {
+    version = rc
+  }
+
+  let ubuntu: string
+  // ubuntu-version is specified
+  if (version.includes("ubuntu")) {
+    ubuntu = version
+  } else if (version !== "") {
+    ubuntu = UBUNTU[version]
+  } else {
+    // default to the maximum vresion
+    ubuntu = UBUNTU[MAX_UBUNTU]
+  }
+
+  const prefix = "clang+llvm-"
+  const suffix = `-x86_64-linux-gnu${ubuntu}.tar.xz`
+  if (semverLte(version, "9.0.1")) {
+    return getReleaseUrl(version, prefix, suffix)
+  } else {
+    return getGitHubUrl(version, prefix, suffix)
+  }
+}
+
+/** The LLVM versions that were never released for the Windows platform. */
+const WIN32_MISSING: Set<string> = new Set(["10.0.1"])
+
+/** Gets an LLVM download URL for the Windows platform. */
+function getWin32Url(version: string): string | null {
+  if (WIN32_MISSING.has(version)) {
+    return null
+  }
+
+  const prefix = "LLVM-"
+  const suffix = semverLte(version, "3.7.0") ? "-win32.exe" : "-win64.exe"
+  if (semverLte(version, "9.0.1")) {
+    return getReleaseUrl(version, prefix, suffix)
+  } else {
+    return getGitHubUrl(version, prefix, suffix)
+  }
+}
+
+/** Gets an LLVM download URL. */
+function getUrl(platform: string, version: string): string | null {
+  switch (platform) {
+    case "darwin":
+      return getDarwinUrl(version)
+    case "linux":
+      return getLinuxUrl(version)
+    case "win32":
+      return getWin32Url(version)
+    default:
+      return null
+  }
+}
+
+/** Gets the most recent specific LLVM version for which there is a valid download URL. */
+export function getSpecificVersionAndUrl(platform: string, version: string): [string, string] {
+  if (!VERSIONS.has(version)) {
+    throw new Error(`Unsupported target! (platform='${platform}', version='${version}')`)
+  }
+
+  for (const specificVersion of getSpecificVersions(version)) {
+    const url = getUrl(platform, specificVersion)
+    if (url !== null) {
+      return [specificVersion, url]
+    }
+  }
+
+  throw new Error(`Unsupported target! (platform='${platform}', version='${version}')`)
+}
+
+//================================================
+// Action
+//================================================
+
+const DEFAULT_NIX_DIRECTORY = "./llvm"
+const DEFAULT_WIN32_DIRECTORY = "C:/Program Files/LLVM"
+
+async function install(version: string, directory: string): Promise<void> {
+  const platform = process.platform
+  const [specificVersion, url] = getSpecificVersionAndUrl(platform, version)
+  core.setOutput("version", specificVersion)
+
+  core.info(`Installing LLVM and Clang ${version} (${specificVersion})...`)
+  core.info(`Downloading and extracting '${url}'...`)
+  const archive = await tc.downloadTool(url)
+
+  let exit
+  if (platform === "win32") {
+    exit = await exec.exec("7z", ["x", archive, `-o${directory}`])
+  } else {
+    await io.mkdirP(directory)
+    exit = await exec.exec("tar", ["xf", archive, "-C", directory, "--strip-components=1"])
+  }
+
+  if (exit !== 0) {
+    throw new Error("Could not extract LLVM and Clang binaries.")
+  }
+
+  core.info(`Installed LLVM and Clang ${version} (${specificVersion})!`)
+  core.info(`Install location: ${directory}`)
+}
+
+export async function setupLLVM(version: string, directoryGiven?: string, cached: boolean = false): Promise<void> {
+  let directory = directoryGiven
+  if (directory === "" || directory === undefined) {
+    directory = process.platform === "win32" ? DEFAULT_WIN32_DIRECTORY : DEFAULT_NIX_DIRECTORY
+  }
+
+  directory = path.resolve(directory)
+
+  if (cached) {
+    core.info(`Using cached LLVM and Clang ${version}...`)
+  } else {
+    await install(version, directory)
+  }
+
+  const bin = path.join(directory, "bin")
+  const lib = path.join(directory, "lib")
+
+  core.addPath(bin)
+
+  const ld = process.env.LD_LIBRARY_PATH ?? ""
+  const dyld = process.env.DYLD_LIBRARY_PATH ?? ""
+
+  core.exportVariable("LLVM_PATH", directory)
+  core.exportVariable("LD_LIBRARY_PATH", `${lib}${path.delimiter}${ld}`)
+  core.exportVariable("DYLD_LIBRARY_PATH", `${lib}${path.delimiter}${dyld}`)
+}
diff --git a/src/main.ts b/src/main.ts
index 32df0533..5e8a6c02 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -25,6 +25,12 @@ export async function main(): Promise<number> {
     if (ninjaVersion !== undefined) {
       await setupNinja(ninjaVersion, setupCppDir)
     }
+
+    // setup llvm
+    const llvmVersion = maybeGetInput("llvm")
+    if (llvmVersion !== undefined) {
+      await setupLLVM(llvmVersion, setupCppDir)
+    }
   } catch (err) {
     core.error(err as string | Error)
     core.setFailed("install-cpp failed")