Ni-Mn based Heusler alloys are magnetic multifunctional materials currently under intense research efforts thanks to their unique coexistence of a reversible structural transformation and magnetically ordered states. Magnetic field induced giant reversible mechanical deformations are promising for new-concept sensors and actuators. Giant caloric effects, triggered by magnetic fields, mechanical stress or pressure, make them promising as novel refrigerants for solid state refrigeration. The structural and magnetic properties of these materials (critical temperatures, magnetic order and entity of the effects) can be finely tuned by composition in a wide range of substitutions: in this sense the degree of atomic order and chemical homogeneity are key parameters. Taking control of these aspects is mandatory for further development and for exploiting these materials in practical applications