A sterilization system having a controllable (e.g. adjustably modulatable) non-ionising microwave radiation source for providing microwave energy for combining with a gas (e.g. an inert gas or a mixture of inert gases) to produce atmospheric low temperature plasma for sterilizing biological tissue surfaces or the like. A plasma generating region may be contained in a hand held plasma applicator. The system may include an impedance adjustor e.g. integrated in the plasma applicator arranged to set a plasma strike condition and plasma sustain condition. The gas and microwave energy may be transported to a plasma generating region along an integrated cable assembly. The integrated cable assembly may provide a two way gas flow arrangement to permit residual gas to be removed from the surface. Invasive surface plasma treatment is therefore possible. The plasma applicator may have multiple plasma emitters to produce a line or blanket of plasma.