When we discuss databases, either relational or non-relational, transactions are one of the most important considerations for ensuring data integrity or dealing with concurrent tasks. Transactions also play an important role when handling database errors and avoiding inconsistent states. Transactions are an integral part of relational databases. Although NoSQL databases generally do not support transactions, there are some that enable transactions with the help of a transaction manager. Similarly, HBase provides transaction support by using Apache Tephra as its transaction manager. In this chapter we will see how Phoenix supports transactions.