Formulation studies of nano- and microparticles are a rapidly developing area in pharmaceutical sciences. Bioavailability of poorly water-soluble drugs may be increased by administrating them as nanoparticle formulations. Drug targeting to specific body sites has also been studied intensively (e.g. cancer chemotherapy). In order to ensure the repeatability of the formulation processes and the efficacy/ stability of the formed particles, thorough characterization of the formulations and particles is crucial. The importance of analytical techniques and even during the process analysis has been highlighted by drug authorities (e.g. FDA) with the PAT approach. Minor deviations, e.g., in particle size/shape, surface charge or aggregation tendency, may play a significant role in their behavior in the body. The very small size of the nanoparticles imposes extra demands for the characterization techniques. In this review, the most commonly used and most important analysis methods to characterize the micro- and nanoparticles are discussed with critical view on the applicability and limitations of the methodologies. Some techniques are well known for the researchers in the small particle area (e.g. microscopic techniques, thermal analysis, zeta potential, dissolution rate), but also more rarely used and new techniques (e.g. surface tension/pressure measurements, spectroscopic methods) are taken into account.