This white paper gives a parts list and step-by-step instructions for building an inexpensive and powerful laser-coupled-fiber system for in vivo use. Please note, part numbers for products are liable to change at any time; contact the manufacturer for updates, and please notify the authors of this white paper as well. Feedback always welcome! NOTE: Unless you are an expert at optics (and even if you are) we highly recommend that you use, or at least first consider, the alternative protocol, “Very Simple Off-The-Shelf Laser and Viral Injector Systems for In Vivo Optical Neuromodulation.”