Do I own the IP created by a contractor?

Good evening, everybody!

I am working with a team of IT and Marketing specialists on an app-development project, which we intend to monetize and turn into a successful venture. We do not have the luck to count a lawyer among our members so I am very interested in this "Ask an Expert" feature.

Soon we will start farming out some of the work to third-party contractors. I would like to know: If I hire someone to work for me on a clearly defined project, do I automatically own the Intellectual Property that is created by the contractor? I assume it is probably not that simple, so what kind of steps do I have to take?

Thank you very much!