Yes, you should try to get letters of support from relevant business contacts who have credibility in the field you are working in. For instance, you may be applying for a grant in clean energy based on research from your Ph.D. work at a university. You may have collaborated with a faculty member in another university, or a corporate sponsor who funded this research. A letter of support from either the faculty member or a leader within the corporate sponsor would be very helpful. The letter does not need to be overly specific; all it needs to do is acknowledge how the other party worked with you and how they know you are the best person / best company possible to lead this research effort.
This article builds on content developed by the Martin Trust Center for MIT Entrepreneurship for MIT's Orbit Knowledgebase and is licensed under CC BY-NC-SA 4.0.