To understand the complexity of the brain, connectome and transcriptome maps of high resolution are being generated, but an equivalent catalogue of the brain proteome is lacking. To provide a starting point, we have performed an in-depth proteome analysis of the adult mouse brain, its major regions and cell types, which resulted in the so far largest collection of cell-type resolved protein expression data of the brain. Comparisons of the 12,934 identified proteins in oligodendrocytes, astrocytes, microglia and cortical neurons with deep sequencing data of the transcriptome indicated deep coverage of the proteome. We identified novel protein makers for different cell type and brain regions. These were validated either directly such as in case of cell types or by comparative analysis against Allen mouse brain atlas. The utility and the power of the resource were demonstrated by the identification of Lsamp, an adhesion molecule of the IgLON family, as a negative regulator of myelination in a subpopulation of neurons. Our in-depth proteome analysis of CNS cell types provides a framework towards a system-level understanding of cell type diversity in the CNS and serves as a rich resource to the neuroscience community for the better understanding of brain development and function.