How I can migrate a Persistence Disk from one project to another, in Compute Engine?

If you want to copy (non-root) persistent disk, do the steps below:

1. Go to Google Developer Console and detach <disk-name> disk from the machine.
2. Use gcloud command-line utility to switch to the old project:
   • gcloud config set project <old-project>
3. Create an image of the <disk-name> disk:
   • gcloud compute images create <image-name> --source-disk=<disk-name> --source-disk-zone=<zone>
4. The output of the above command will give you a fully qualified link to the image (in the form https://www.googleapis.com/compute/v1/projects/<project-name>/global/images/<image-name>). Alternatively, run: gcloud compute images list --no-standard-images --uri | grep <image-name> to find the link.
5. Switch to the new project:
   • gcloud config set project <new-project>
6. Create a new disk from the image:
   • gcloud compute disks create <new-disk-name> --image=<link-to-the-image> --zone=<zone>

As above Mike Lutz's answer, except gcutil is now deprecated, but the 2nd command can also be done with gcloud compute instance are:

1) create your image from you PD (NB! read first! https://cloud.google.com/compute/docs/images#creating_an_image_from_a_root_persistent_disk)

$ gcloud compute images create [example-image] --source-disk [example-disk] --source-disk-zone ZONE --project="old-project-name"

2) Instantiate the image in the new project (goes without saying but you must have access to both projects)

$ gcloud compute instances create [example-instance-1] --project=[new-project-name] --image="https://www.googleapis.com/compute/v1/projects/[old-project-name]/global/images/[image-name]" --boot-disk-size [XXXGB] --machine-type=[machine-type] --network="default" --zone=[datacenter-zone] 

• you can see the URL of your image in the Images tab under "Equivalent REST"

For additional instance config options see: https://cloud.google.com/sdk/gcloud/reference/compute/instances/create

In case anyone else lands here from a google search, today you can create a disk in one project directly from a snapshot in another project, without creating any temporary physical disks or images.

1. Create snapshot: gcloud compute disks snapshot your-disk-name --snapshot-names=your-snapshot-name --project=source-project --zone=source-zone

2. Describe the snapshot and find the selfLink: gcloud compute snapshots describe your-snapshot-name --project=source-project

3. Use the selfLink instead of a snapshot name when creating a disk in the new project: gcloud compute disks create your-new-disk-name --project=destination-project --zone=destination-zone --source-snapshot=https://www.googleapis.com/compute/v1/projects/source-project/global/snapshots/your-snapshot-name