 chapter aims to provide an introduction to synchronization for nonexperts and an over- view of the sync requirements and implementation for O-RAN. It is impossible in a single chapter to even really scratch the surface of this subject and hence a large amount of detail has been intentionally overlooked. To get broader, and more in-depth, information on the topic, there are a number of sources that can be explored: Solution vendors whitepapers and presentations-Many players in the space, both the semiconductor and software companies supplying the building blocks, such as PLLs, and Chapter 8 Synchronization in open radio access networks the system level solution providers, selling the likes to PTP Grandmasters, have libraries of material available. Some of this will be very product-specific, but much of it also contains more widely applicable material. Synchronization conferences-There are a number of annual conferences held that specialize in just synchronization. Two of these-WSTS (Workshop on Synchronization and Timing Systems) held in the United States, and ITSF (The International Timing and Sync Forum) in Europe-specialize in providing presentations targeting real-world, topical, applications such as O-RAN synchronization. Other conferences, such as ISPCS, are more technology-focused in their scope. This page intentionally left blank Software performance If there ever was a "how long is a piece of string" question, it would be "how good will my software perform on this system." Software performance greatly depends on the amount of time spent both on architecting an efficiency environment in which software is set up to run fast (say, optimizing the processing flow for data locality, providing user-space drivers, SO on), and software application stack optimization itself. Many developers tend to treat per- formance as an afterthought and respond with a "just use more cores" answer if perfor- mance is not at the desired level. We try to counter this with up-front analysis of what performance should be achievable