Single-particle cryo-EM has emerged as a technique capable of studying challenging systems that otherwise defy structural characterization. We are using cryo-EM in the study of complex gene expression machinery for which only small amounts of sample are available, and that suffer from both compositional and conformational mixtures. We have been able to define the structure of the human transcription pre-initiation complex in three different sequential steps through the transcription initiation process. We have also recently obtained the structure of human TFIIH, a complex essential both in transcription initiation and in base excision DNA repair. A major effort in our lab has been to describe the structure and dynamics of human TFIID, a complex of over 1 MDa that binds to DNA and recruits the rest of the transcription initiation machinery. TFIID is composed of TBP (TATA-binding protein) and 13 TAFs (TBP-associated factors). Our recent studies provide the first, full subunit organization within this large complex. I will also present our results concerning the structural dynamics of human TFIID and how they relate to the critical process of core promoter recognition and binding, most significantly, how dynamics of one of TFIID structural lobes is used for the loading of TBP onto the upstream DNA core promoter region.