Currently many safety-critical systems are being built. Safety-critical systems are those software systems where a single failure or hazard may cause catastrophic consequences. Therefore, safety is a property which must be satisfied for safety-critical systems. This research develops techniques to address two areas of software safety analysis in which structured methodologies have been lacking. The first contribution of the paper is to define a top-down, tree-based analysis technique, the Fault Contribution Tree Analysis (FCTA), that operates on the results of a product-family domain analysis. This paper then describes a method by which the FCTA of a product family can serve as a reusable asset in the building of new members of the family. Specifically, we describe both the construction of the fault contribution tree for a product family (domain engineering) and the reuse of the appropriately pruned fault contribution tree for the analysis of a new member of the product family (application engineering). The second contribution of the paper is to develop an analysis process which combines the different perspectives of system decomposition with hazard analysis methods to identify the safety-related scenarios. The derived safety-related scenarios are the detailed instantiations of system safety requirements that serve as input to future software architectural evaluation. The paper illustrates the two techniques with examples from applications to two product families in Chapter One and to a safety-critical system in Chapter Two.