Safety-critical systems, such as those in the avionics, automotive, power, space, and medical industries, are predominantly driven by real-time embedded software and are often referred to as high-integrity real-time systems (HIRTS). In these systems, safety is of paramount importance. Safety is broadly defined as freedom from accidents and loss. When no safe alternative to normal service exists, a system must be dependable to be safe, that is, it must have reliable ways to deliver a certain quality of service. Our collaborations with industrial partners have focused on HIRTS modeling techniques. Initially, we explored the potential benefits that the most successful software architecture and modeling approaches could bring to the safety-critical domain. We subsequently designed the architecture information modeling language. AIM lets us exploit the available technologies from the same platform and thus provide stronger support for the safety case. A safety case, a key element in HIRTS certification, typically consists of a high-level argument and supporting evidence. The HLA sets the principles on which the design is based and reasons why the design should satisfy the safety requirements.