diff --git a/README.md b/README.md
index bdf9f5d..43cdfbf 100644
--- a/README.md
+++ b/README.md
@@ -23,7 +23,21 @@ $ pip install -r requirements.txt
 
 ## Building the box
 
-TODO
+Just execute:
+
+```sh
+$ packer build packer.json
+```
+
+_Note: It will take at least roughly 5 - 10 minutes for the ISO to get preseeded ("pre-provisioned") by the Debian installer, hence the rather long timeout/waiting period before packer actually starts provisioning. If you're unsure whether there is any progress change the values `headless` in the `packer.json` from `true` to `false` and re-run the process. This will give have VirtualBox show you the output of the console the ISO is running on._
+
+This will preseed the Ubuntu ISO image for Ubuntu Xenial 64bit with a couple of sane defaults and packages. Afterwards, the Ansible provisioner is run using the playbooks from the [mastodon-ansible](https://github.com/moritzheiber/mastodon-ansible) repository.
+
+In the end you should have a box in `builds/` with all the required components installed you can run directly in Vagrant.
+
+## Submitting to Atlas
+
+tbd
 
 ## Testing
 
diff --git a/packer.json b/packer.json
index 5de4de9..267d01d 100644
--- a/packer.json
+++ b/packer.json
@@ -1,5 +1,10 @@
 {
-  "provisioners": [],
+  "provisioners": [
+    {
+      "type": "ansible",
+      "playbook_file": "ansible/playbook.yml"
+    }
+  ],
   "builders": [
     {
       "type": "virtualbox-iso",
@@ -32,7 +37,7 @@
       "boot_wait": "10s",
       "disk_size": 10000,
       "guest_os_type": "Ubuntu_64",
-      "headless": false,
+      "headless": true,
       "http_directory": "preseeds",
       "iso_urls": "http://releases.ubuntu.com/16.04/ubuntu-16.04.2-server-amd64.iso",
       "iso_checksum_type": "sha256",