The mitotic chromosomes of the baker's yeast, Saccharomyces cerevisiae, cannot be visualized by standard cytological methods. Only the study of meiotic bivalents and the synaptonemal complex and the visualization of chromosome-sized DNA molecules on pulsed-field gels have provided some insight into chromosome structure and behavior. More recently, advanced techniques such as in situ hybridization, the illumination of chromosomal loci by GFP-tagged DNA-binding proteins, and immunostaining of chromosomal proteins have promoted our knowledge about yeast chromosomes. These novel cytological approaches in combination with the yeast's advanced biochemistry and genetics have produced a great wealth of information on the interplay between molecular and cytological processes and have strengthened the role of yeast as a leading cell biological model organism. Recent cytological studies have revealed much about the chromosomal organization in interphase nuclei and have contributed significantly to our current understanding of chromosome condensation, sister chromatid cohesion, and centromere orientation in mitosis. Moreover, important details about the biochemistry and ultrastructure of meiotic pairing and recombination have been revealed by combined cytological and molecular approaches. This article covers several aspects of yeast chromosome structure, including their organization within interphase nuclei and their behavior during mitosis and meiosis.