The DNA replication checkpoint, also known as the intra-S or S-phase checkpoint, plays a central role in ensuring the accuracy of DNA replication. When replication is impeded by DNA damage or other conditions, this checkpoint delays cell cycle progression and coordinates resumption of replication with DNA repair pathways. One of its critical functions is to stabilize stalled replication forks in a replication-competent state, presumably by maintaining proper assembly of replisome components and preserving DNA structures. Here we describe a series of assays used to study the replication checkpoint. These assays allow us to investigate the specific functions of proteins involved in the replication checkpoint in fission yeast.