The human genome is subject to numerous endogenous and exogenous stresses that cause a variety of DNA damage and has thus evolved a complex DNA damage response (DDR). Within this DDR are a number of DNA repair pathways, which have evolved to repair different types of DNA damage. One such mechanism is the Fanconi Anaemia (FA) pathway, which repairs interstrand crosslinks (ICLs). Crucial to the activation of this pathway is the recognition of the ICL, and the subsequent recruitment and ubiquitination of the FANCD2/FANCI heterodimeric complex. This complex is site-specifically monoubiquitinated on each protomer which is essential for the removal of the ICL and the subsequent repair of DNA. In addition, the deubiquitination of the monoubiquitinated FANCD2/FANCI has been shown to be necessary for the FA pathway to function. The FA pathway is a complex pathway and many open questions remain to be answered, including the mechanism of recognition of the ICL, how the FANCD2/FANCI complex is ubiquitinated, and whether it is ubiquitinated as a heterodimeric complex or sequentially as single substrates, as well as whether ubiquitination and deubiquitination occur on or off DNA in vivo. In addition, it has been postulated that upon ubiquitination of the complex, FANCD2/FANCI undergo a conformational change locking onto DNA, perhaps necessary for the recruitment of downstream repair factors. Here, in vitro investigation of the key FANCD2/FANCI complex was undertaken, including studies on whether monoubiquitination is stimulated by DNA, and whether deubiquitination of the monoubiquitinated FANCD2/FANCI occurs on or off DNA. Work towards the structures of FANCD2/FANCI and possible ubiquitination intermediates, monoubiquitinated-FANCD2/FANCI and monoubiquitinated-FANCI/FANCD2 via negative staining electron microscopy (EM) and cryo-EM is also described. Furthermore, the investigation of filament formation upon ubiquitination of FANCD2/FANCI was carried out. Additionally, a previously identified ICL sensor protein, UHRF1, was also investigated. Specifically, the effect of UHRF1 on the monoubiquitination of FANCD2/FANCI was explored in vitro as well as progress towards the first full-length UHRF1 structure via negative staining EM and cryo-EM is described.