This chapter (Partially based on: Levin MS (2013) Towards multistage design of modular systems. Electronic preprint, p 13, June 19, 2013. http://arxiv.org/abs/1306.4635 [cs.AI]) addresses frameworks for multistage design of composite (modular) systems (i.e., designing a system trajectory). Mainly, the resultant system trajectory is examined as chain of system versions. In addition, system trajectories based on tree or digraph are considered. Illustrative numerical examples correspond to multistage design of development trajectory for start-up company, combinatorial planning of medical treatment, and multi-domain problems (e.g., joint medical diagnosis and medical treatment plan, joint system testing and system maintenance).