Hey there, I am reading up on transactions in mysql and am not sure whether I have grasped something specific correctly, and I want to be sure I understood that correctly, so here goes. I know what a transaction is supposed to do, I'm just not sure whether I understood the statement semantics or not. So, my question is, is anything wrong, (and, if that is the case, what is wrong) with the following: By default, autocommit mode is enabled in mysql. Now, SET autocommit=0; will begin a transaction, SET autocommit=1; will implicitly commit. It is possible to COMMIT; as well as ROLLBACK;, in both of which cases autocommit is still set to 0 afterwards (and a new transaction is implicitly started). START TRANSACTION; will basically SET autocommit=0; until a COMMIT; or ROLLBACK; takes place. In other words, START TRANSACTION; and SET autocommit=0; are equivalent, except for the fact that START TRANSACTION; does the equivalent of implicitly adding a SET autocommit=0; after COMMIT; or ROLLBACK; If that is the case, I don't understand http://dev.mysql.com/doc/refman/5.5/en/set-transaction.html#isolevel_serializable - seeing as having an isolation level implies that there is a transaction, meaning that autocommit should be off anyway? And if there is another difference (other than the one described above) between beginning a transaction and setting autocommit, what is it? Thanks a lot in advance for your help!