Your digital files belong to you but the client may have rights to them as well.
A typical situation: "I finished a project for a client and now he is asking me to turn over all the digital copies of the work I did, the original application files and graphics. If I did that, couldn't he just take all my digital files to another designer and cut me out of the loop when he needs additional work done?"
Ownership of the ArtworkIf your contract specified that the client was paying for the original files then you are obligated to turn them over. Since it increases the possibility that you'll lose your chance at repeat business from this client, I hope you charged extra for turning over the files. What does your contract say?
As a minimum, a freelance design contract should specify ownership of the artwork — including original digital files — as well as ownership of preliminary designs.
Oops, There's Nothing in the Contract About File OwnershipIn that case, you can weigh your options. If you refuse to turn over the files what is the risk that you'll lose goodwill and future business from this client? If that's a risk you don't want to take you may want to go ahead and give them the files.
Willingly or unwillingly you can still charge the client a fee to cover media costs and the time required to transfer the files to disk. If the client requires the files in formats other than what you have them in, charge for the file conversion service.
And count this as a lesson learned. Rework your contract to include digital file ownership details for all future projects with your other clients.