This chapter presented an overview of building blocks for modern high-availability architectures for network resources and services. As discussed in this chapter, HA is an endeavor that involves thorough architectural planning; planning for network elements, links, and server resources; and a thorough consideration of both hardware and software. Issues such as load balancing, failover concepts, redundancy protocols, and heartbeat were discussed. Toward the end of this chapter, the art of clustering was introduced and address takeover approaches were explained. An introduction to IRDP focusing on gateway discovery and redundancy concluded the chapter.