This manuscript reviews our progress on investigation of composition selection, phase transitions, sintering, and phase diagram of lead-free systems based upon (K,Na)NbO3 [KNN]. For composition selection, weight ratio rule can be used in piezoelectric ceramics with perovskite structure. It was found that coexistence of two phases at room temperature in polymorphic systems leads to outstanding piezoelectric response. The effect of tetragonal phase fraction on piezoelectric response was investigated and it was found that maximum piezoelectric response occurs at 70%. In order to control the microstructure, sintering behavior was modeled and explained using temperature-dependent SEM images under varying sintering conditions. Moreover, it was found that particle size distribution should be controlled to get well-sintered specimen. In addition to KNN, (Bi,K)TiO3 [BKT] and BaTiO3 [BT] based ceramic compositions were also studied to develop new lead-free piezoelectric materials. From combination of these studies, we have developed modified lead-free systems exhibiting wide range of dielectric and piezoelectric properties suitable for applications in sensors, actuators, and capacitors.