How can we accurately estimate the population density of wild animals? How can we reliably assess the spatial differences in the density between several areas? These questions are commonly important for people engaging in wildlife monitoring, including field ecologists, conservation officials and area managers. The REST model is one approach to estimating the density of unmarked animal populations exclusively from camera trap data. This handbook provides a protocol for beginners who are relatively inexperienced in camera trapping and unfamiliar with statistics. Reflecting on our own experience, this manual assumes terrestrial mammal species in tropical rainforests (e.g., forest ungulates and large rodents) as monitoring targets. We first explain the formula and assumptions of REST briefly. Then, we describe the field and analytical procedures required for density estimation with REST.