This chapter covers broadcast communication abstractions. These are used to disseminate information among a set of processes and differ according to the reliability of the dissemination. For instance, best-effort broadcast guarantees that all correct processes deliver the same set of messages if the senders are correct. Stronger forms of reliable broadcast guarantee this property even if the senders crash while broadcasting their messages. Even stronger broadcast abstractions are appropriate for the arbitrary-fault model and ensure consistency with Byzantine process abstractions.