Transcription in eukaryotes is regulated by many enzymes that influence the nuclear organization of DNA in chromatin. Several of these enzymes regulate histone modifications. These modifications function as a platform for assembly of protein complexes that influence chromatin structure. Dynamic changes between chromatin states that facilitate or inhibit transcription are important in the transcriptional regulation of pathways controlling floral induction in response to environmental and developmental signals. This review focuses on the mechanistic aspects of histone modifications and chromatin changes at flowering-time genes and how these relate to the initiation of flowering.