Deterministic transmission planning is based on deterministic assumptions, by planning for a single forecasted set of conditions. The issue of adaptability in transmission and generation expansion planning has become important for planners in order to deal with future uncertainties. Adaptability is "the ability to change (or be changed) to fit changed circumstances" [ ]. Adaptability planning helps mitigate losses in unforeseen situations and exploit opportunities in expected situations. Adaptability also provides the opportunities to take alternative actions after events unfold. Adaptable plans can help reduce future costs and time, and it also reduces complexity associated with possible future changes to the existing system. In order to assess the value of adaptable planning in this dissertation, our approach is illustrated using the IEEE 24 bus system and the Iowa system. Our adaptable planning shows there is benefit in incorporating uncertainty into power system planning when compared to deterministic planning which is the conventional approach.