Synthesis issues at the process development stage generate large combinatorial problems whose solution has a profound effect on the feasibility and optimality of the resulting processing schemes. This paper deals with the formulation of various such synthesis problems, examines their principal characteristics and how these scope the solution procedures. In particular, the paper addresses the following issues and methodologies: How topological characteristics of the search space define patterns which can be exploited for the systematic generation of attractive chemical production schemes. What characteristics define targeting procedures and evolutionary syntheses for the design of molecules with desired physical properties. How a knowledge-based expert system is designed for the synthesis of feasible and attractive biochemical pathways.