This research seeks to reduce the existing gap in destination marketing knowledge by explaining tourists’ loyalty from an integrated perspective whereby several variables intervene in its formation. The study investigated the utility of applying the Investment Model (Rusbult, 1980a; 1983) to reveal the processes underlying loyalty formation, integrating the findings of loyalty antecedents from marketing and tourism literature, namely, satisfaction, motivations, variety seeking, commitment, investment size and income. Moreover, to reinforce the understanding of loyalty process patterns and validate the determinants that persist under different contexts and over the years, this research has examined whether the destination loyalty model was invariant across different groups (Lisbon and Faro and the Azores and Madeira, as well as, over the IATA years 2009/10 and 2010/11). The model was validated empirically by employing a sample of 8991 questionnaires collected for the INITIATIVE:pt1 study. Structural Equation Models (SEM) using AMOS 19 were developed to examine the relationships between the various variables in the model. The results indicates that motivation is influencing tourists’ satisfaction level, which in turns, determines the level of commitment. The investment tourists need to make, negatively influence tourists commitment and both explain loyalty from an attitudinal or behavioural perspective. Loyalty is explained by the promise of tourists to risk new destinations (variety seeking). The variety seeking is explained by motivations and satisfaction, but it is not influenced by the tourist family income. The findings suggest that the Investment Model, (Rusbult, 1980a) worked in the context of destinations loyalty. Finally, it was found that some of the model relations exert differential effects between the various groups being more evident on the in Azores and Madeira and on the longitudinal perspective (2009/10 and 2010/11). This results provide an opportunity for new research to be undertaken on developing a comprehensive destination loyalty model that not only contributes to progress in knowledge on the processes which produce loyalty in tourists, but also to progress in management techniques and marketing strategies to tackle such a challenge: gaining and retaining destination visitors.