In this post, I summarize the study of the paper Time, Clocks, and the Ordering of Events in a Distributed System authored by Leslie Lamport published on Communications of the ACM in 1978. The paper dives into the fundamental topics “time and clock” in the distributed system, and proposed several important concepts such as Happened-Before, Logical Clocks, Physical Clocks and State Machine Replication. It is definetely one of the “Must-Read” classic paper in distributed system area.