\({\varvec{s}}\) \(\text{p}\) This chapter presents the nearly free electron model for metals in groups I–IV, characterized by s and p conduction electrons outside closed shells. Starting from the Sommerfeld free electron gas, the model is extended to include a weak periodic potential. The “free-electron-like” behavior of conduction electrons is explained through the Pauli exclusion principle and screening effects, which reduce the influence of ion cores. These concepts provide a basis for understanding electrical conduction in metals and semiconductors.