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It is well known that GPS, when used outdoors, meets all the location requirements for E911 as well as commercial location based services. The problem, till now, has been making GPS work indoors. This paper addresses the technical issues confronting indoor GPS, and shows, in clear and simple terms, how GPS technology can, and has been brought inside. We begin with a theoretical overview of the technology, and then show how the theory has been reduced to practice in a single baseband chip that performs massively parallel correlations to detect the GPS signal at power levels 30dB (one thousand times) below those found outside. The paper also addresses the role of the wireless operator in providing aiding information to the GPS receiver, the industry standards that have emerged, and the issues faced by anyone evaluating this new technology. Finally, the paper presents real world results showing the performance of Global Locate’s Indoor GPS hardware implementation.