This dissertation examined certain distal and proximal relational factors and emotional capabilities of individuals in therapeutic programs in Greece. The three studies aimed to extend existing work by examining links between distal (child abuse reports) and proximal (adult attachment, social support) relation factors with psychological health outcomes of substance users in addiction treatment programs. The results from the three studies supported the view that: a) distal (childhood maltreatment) and proximal (attachment organization) relational factors are important predictors of substance users’ well-being; b) proximal factors (anxious attachment) mediate effects of abusive experiences; c) emotional capabilities and specifically regulatory processes have a prominent role as mediators of relational factors on substance users’ well-being.