This chapter describes the inverse planning basics. An ideal plan would have the prescribed isodose conform to the planning target volume (PTV) while having a minimal dose to the nearby organs at risk (OAR). To obtain an optimal plan, inverse planning includes the following three key components: planning objectives; cost function that measures goodness of a plan; and optimizer to minimize the cost function. The use of the gradient search algorithm and dose-volume-based cost function, optimization for a complex case with numerous sensitive structures requires multiple, manual iterations, also termed staged planning or warm starts. On the first stage planners start with planning objectives for the PTVs, critical structures, and the ring structure. On the second round optimization, without resetting intensity modulated radiation therapy, the planners add more planning objectives for additional OARs. Modern treatment planning systems are implementing advanced planning tools such as auto-planning, multi-criteria optimization, and knowledge-based planning.