Encapsulation in micro- and nanoparticles is an effective method for protection and controlled release of liquid and solid substances. There are numerous preparation methods available for producing particles and capsules. An important issue is the reliable and reproducible preparation by industrially scalable methods. The products and the processes must be technically feasible and affordable. The emulsion based method called “miniemulsion polymerisation” is an inexpensive process which is suitable for up-scaling to industrial production. Both liquids and solids can be encapsulated by miniemulsion polymerisation, provided that they do not interfere with the polymerisation process. The key feature of the miniemulsion process is the co-stabilizer added to the droplet phase before emulsification, as it stabilizes the system against Ostwald ripening. Miniemulsion polymerisation has been applied successfully for encapsulation of active compounds for agricultural products, cosmetics, personal care and household products, as well as in biomedical applications. Examples of encapsulated substances are liquid crystals, magnetic iron oxides, insect repellents and fragrances. Our current aim is to adapt the method for encapsulation of drugs and diagnostic markers in biocompatible and biodegradable polymers. The miniemulsion polymerisation technique has been applied to prepare nanoparticles of the biodegradable polymer poly(butyl-2-cyanoacrylate) (PBCA). For medical application as drug delivery system, characteristics of the nanoparticles surface are crucial to avoid clearance by the reticuloendothelial system. Therefore, to inhibit unspecific binding to cells in general, and to prevent an uptake by monocytes, nanoparticles having poly(ethylene glycol) chains at the surface have been synthesized.