Develop the project outline. Before you begin the formal writeup of the project proposal, you need to have a specific step-by-step plan.
Obtain faculty agreements. Students need a supervisory faculty member from each discipline covered by the project. These faculty members must agree to work with each other and cooperate on the project. The same is true for a university project. Each discipline must have a coordinating faculty member who agrees to be part of the project and to facilitate it cooperatively. These commitments can sometimes be the most difficult part of an interdisciplinary project, so be sure they are in place before you write a proposal.
Complete a literature review. Develop a justification for the project through a summary and analysis of the most important information available on the topic. For student projects, the literature review shows what research has been done in the past on this topic and creates the argument for this new project that hasn't yet been done. For a university project, this section provides support for the project. There may be literature in the form of books or journal articles to support the idea, or there may be similar projects at other universities.
Write the procedure for the project. List each step of the project and the purpose of each step. Note how each discipline comes into play during the research and what theory or technique is supported by the methodology. This section also lists all the equipment and expertise that will be needed to complete the project, the time frame anticipated for completion, the survey instrument -- if applicable -- the budget and the division of oversight between the disciplines.
Write the introduction to the proposal. The introduction section provides a justification for the project. It tells three basic things: what the project is, why it is important to do and the goals or desired outcome of the project. This section is written last because all the other work you have just done gives you the information needed for the introduction.
Complete finishing touches. Your formal proposal will need a bibliography or works cited page and will likely need a cover page, abstract and table of contents as well. Check with the specific university for requirements.
Allow for faculty review. Prior to official submission of an interdisciplinary proposal, it is a good idea to allow each faculty advisor in each discipline to review the suggested proposal. Gather any ideas or concerns and address them if possible. You want the full support of your team when it comes time for pushing your proposal through.