Precise expression of transgenes in C. elegans can be used to understand gene regulation, control cells, or as a starting point for genetic screens. Insertion of single-copy transgenes into well-defined safe-harbor locations is useful when consistent expression levels are required (e.g., to compare expression from different transgenes) or when expression is desired in germ cells. Here, we describe a detailed protocol for inserting single-copy transgenes using Modular Safe-harbor Transgene Insertion (MosTI) and a heat-shock inducible Cas9 expressed from a co-injected plasmid. Inducible Cas9 expression has the advantage of requiring few injections, and many independent single-copy insertions can be generated from a single array line.