This paper examines the effects of childhood maltreatment on attachment and development. Humans are social beings; connection is at the core of human behavior. This social nature is what drives the need to form relationships with others. Relationships help humans learn and understand the social world around them relatively safely and securely. However, to ensure that these relationships bring safety and security, the ability to do so must be established during the first 18 months of children’s lives (Kennedy & Kennedy, 2004). The relationships humans form are based on how they establish attachments, or emotional and long-term bonds and relationships, to a primary caregiver or parent as children (Bowlby, 1969). These primary attachments include secure, anxious-preoccupied, insecure-avoidant, or fearful-avoidant attachments and can have significant effects on individuals or emerging adults in early adulthood (ages 18-25). Primary attachments act as a safe and organized view of how human interactions and relationships work and act as a secure base for children to explore and successfully understand the social world around them (Feeney & Noller, 1996). However, this depends on whether or not safety, a secure base, and an organized view of relationships are formed between the caregiver and child during the first 18 months of the child’s life. Moreover, if a child experiences maltreatment such as abuse and neglect from primary caregivers during their first 18 months of life, it can severely affect what type of attachment style is formed and how development occurs in early adulthood (Connell-Corrick, 2011). Therefore, to thoroughly understand how childhood maltreatment affects attachment and development, an overview of both attachment theory and childhood maltreatment, the effects of childhood maltreatment on both attachment and development, and the importance of protective factors, interventions, and preventions will be discussed.