What do you do if you have like a 10 or 20 year gap between your MS and your PhD with respect to getting letters of recommendation? I would eventually like to get my PhD, but I'm pretty sure that a good deal of my professors will be retired by the time I'd like to go for it. Are you supposed to stay in touch with a few professors as long as you have further academic ambitions, or is there some other way to get letters of recommendation, say from your boss or co-workers? This is for a PhD in EE, and I will not be within academia at all. I'd like to just work on my PhD part-time in the future, no matter how long it takes.