All operations within a transaction must route to the same member (i.e. %primary%) Read and write concerns are specified once, when starting a transaction While many operations are supported, there are some restrictions (e.g. DDL) Databases and collections must exist prior to starting the transaction Cursors created outside a transaction cannot be used within, and vice versa Transactions and retryable writes (i.e. %retryWrites=true%) are mutually exclusive