The aim of this chapter is to introduce three aspects of attachment theory (Bowlby, 1997 [1969]): the concept of behavioural systems, which Bowlby (1997 [1969]) proposes to explain behaviours; how the attachment behavioural system is developed from early interaction experiences with primary caregivers; and how the development of the attachment behavioural system shapes individuals’ internal working models of self, others and the broader social environment that continue to guide an individual's attitudes, beliefs and behaviours in later life.

The chapter first reviews the concept of the behavioural system – the core concept of attachment theory. Bowlby (1997 [1969]) proposed this construct to explain how instinctive behaviours are governed by specific set goals for achieving evolutionary adaptiveness. This concept is the key to understanding proactive behaviour as this book conceptualizes proactive behaviour as a form of exploration behaviour governed by the exploration behavioural system with the goal of mastering the environment to serve the end goal for survival and reproduction, and then relies on this conceptualization to theorize how attachment styles can shape proactive behaviour.

The chapter then reviews the development and operation of the attachment behavioural system – the core behavioural system whose operation is shaped by the interaction experiences between infants and their primary caregivers. This section elaborates on individual differences in the operation of the attachment behavioural system (that is, attachment styles) that are due to the different earlier interaction experiences. The idea of individual differences in attachment styles is important to the understanding of proactivity because it helps explain how the different operations of the attachment behavioural system shape different operations of the exploration behavioural system, and thus helps explain proactive behaviour.

Finally, the chapter introduces the concept of the internal working model – a cognitive representation of oneself and the external social environment. It describes how an internal working model is developed from early interaction experiences and consolidated over time, and then becomes a part of personality, reflecting individuals’ beliefs, attitudes and expectations in social relationships (see Collins and Read, 1994; Collins and Allard, 2002). Because individuals have different interaction experiences with their primary caregivers, the contents of their internal working models are also different, and these in turn are related to the attachment styles they develop.