Emulsion polymerisations are mostly carried out as (semi-)batch processes in stirred tanks. In ab-initio emulsion polymerisation the product properties in terms of particle concentration and particle size distribution strongly depend on the course of the nucleation stage. The course of the nucleation stage is strongly related to the quality of emulsification and the temperature of the reaction mixture. The influence of temperature on the particle size distribution was investigated for completely isothermal as well as for non-isothermal operation. Reaction calorimetry has been chosen as a tool to define an operating window for control of the nucleation stage in emulsion polymerisation. It was demonstrated that reaction calorimetry is a very poweful tool to define operational details for complete control of the nucleation process in emulsion polymerisation in stirred tanks accurately and quickly. Colloidal stability of the latex is an important issue during the stage of particle growth by simultaneous polymerisation and monomer absorption from the monomer droplets. It was demonstrated that a proper recipe for the production of a colloidally stable latex can be developed in a short time with reaction calorimetry.