The role of particle size reduction and particle engineering is growing considering the design and manufacturing of drug carrier systems. The objective of the review is to summarize and compare the micronization methods based on particle size reduction and which are applied to improve drug dissolution and bioavailability. These methods are effective especially when suitable pharmaceutical excipients are used by cogrinding. Beside formation of engineered particles, milling remains important to design particles with the desired size, shape and surface characteristics.