The physical organization of all eukaryotic genomes is evolutionarily conserved. Histone protein octamers repeatedly wrap genomic DNA into nucleosomes to form long chromatin fibers. Nucleosomes and chromatin function to control occupancy of transcription factors at their DNA target sites to regulate transcription initiation. I will discuss some differences between activating and pioneering transcription factors. I will then present our recent findings on how nucleosomes have profoundly different impacts on the dynamics of these two types of transcription factors, which provide a potential way to define the functional differences between activating and pioneering transcription factor activity.