Software Architecture Comparison Analysis Methods provide organizations with a rationale for an architecture selection process by comparing the fitness of software architecture candidates for required systems. With the lack of data about software architecture, developing comparison methods based on a black box approach is considered very helpful, and architectures can be compared based on a set of criteria derived from the business goals of an organization. A popular method in this context is the Software Architecture Comparison Analysis Method (SACAM) developed by (SEI). This book presents a proposed adaptation of SACAM to be applied in the context of critical socio-technical systems where issues of architecture evolution and maintenance are considered important factors in selecting a strategy to software modernization. The proposed method is called software Architecture Comparison Analysis Method for Critical Systems (SACAM-CS). SACAM-CS is an architecture selection method based on multi-criteria decision analysis. The proposed method has been validated using a suitable case study to compare among two critical systems "check-in systems" used in international airports.