This document summarizes the possible development of human space flight beyond the International Space Station. It describes particularly the present state-of-the-art and prospects of lunar development. The rationale of entering a new phase of lunar development is presented, including the social and political background. The essential functions and associated facilities of an initial lunar base are described. It is shown that the space transportation system, providing the logistic support of a lunar base, is the bottleneck of new evolutionary steps. A feasible schedule and associated detailed cost estimates are presented. Financing strategies and legal restrictions are summarized. The options available such as a 'Lunar Outpost' and/or 'Initial Lunar Base' are discussed using representative examples. A program comprised of ten years development and thirty years of operation, leading to a lunar base with up to 100 people, is recommended as a reference model for future considerations. - This documentation is comprised of 212 pages, 88 tables, 35 figures and 117 references.