Methylotrophic yeasts have attracted increasing interest as useful systems for fundamental research and applied purposes. Hansenula polymorpha in particular has become a preferred organism for the production of recombinant proteins on an industrial scale. Product examples range from therapeutics such as hepatitis B vaccines to industrial enzymes like the feed additive phytase. This book is addressed to researchers and scientists working in the field and provides a comprehensive, up-to-date overview of the present status of Hansenula polymorpha research, applications and methods. Aspects of the organism ranging from systematics, genetics, methanol metabolism and peroxisomal function to its use as a technology platform for the production of recombinant proteins are covered. A detailed chapter on laboratory methods is also included.