Research has confirmed the prevalence of chronicity and multiplicity in childhood maltreatment experiences and the lifespan implications of these victimisations (Bromfield, L. M., & Higgins, D. J., Family Matters, 2005, 38, 2005; Anda et al., 1998; Felitti et al., 2003). The impact of the accumulation of ACEs has been labelled ‘cumulative harm’ (Bromfield et al., Developing Practice: The Child Youth and Family Work Journal, 19, 34–42, 2007). Cumulative harm is defined as “a series or pattern of harmful events and experiences that may be historical, or ongoing, with the strong possibility of the risk factors being multiple, inter-related and co-existing over critical developmental periods” (Bromfield et al., Developing Practice: The Child Youth and Family Work Journal, 19, 34–42, 2007, p. 1). This chapter will explore the broad range of theoretical perspectives which inform our current understanding of cumulative harm, exploring concepts of chronicity, developmental victimology, poly-victimisation and revictimisation. The author will highlight the qualities that characterise cumulative harm and the ways accumulative adversity can manifest across the lifespan.