Among currently classified mental disorders in psychiatry, symptoms of depression and anxiety are among the most reported and prevalent. And yet, a unified consensus of their categorization, predictability, and treatment in psychiatry has remained incomprehensive and controversial. Memes derived from antiquated notions of psychopathology and pop psychology still dominate some public discourse. At the same time, contemporary research psychiatrists struggle in complex and contentious discourse over methodological precision and ontological coherence in diagnosis and classification. Whether rates of anxiety and depression are increasing or an artefact of increased cultural awareness and measurement also remains unknown. Bridging scientific explanations with first-person experiences of depression and anxiety has been perhaps unsurprisingly difficult due to the complexity of internal and external factors, and their interactions. Despite continued resistance, DSM categories of psychopathology still offer pragmatic resources for diagnosis and very often prognosis. Still, they do not answer essential questions regarding variable aetiological trajectories, how specific categories and symptoms interact with each other, or what (if any) adaptive functions such behavioural, emotional, or cognitive features associated with anxiety and low mood in some ranges might ultimately offer. While not universal, interactions between anxiety and low mood are frequent. These will be explored in novel detail and key results from this dissertation will strongly indicate important transdiagnostic mechanisms, potential learning mechanisms, aetiological pathways, cognitive profiles, and specific domains of social feedback which may converge and also separate mood and anxiety dimensions. Several conclusions and outstanding questions for future research are then developed and derived throughout theoretical portions. To progress the understanding of mood and anxiety disorders, this thesis's theoretical and empirical aims are to 1.) Examine the overarching problems in contemporary psychiatry regarding explanation and prediction in mood and anxiety, and offer some potential solutions and novel directions 2.) Analyse some of the central biopsychosocial components within anxiety & mood disorders, their interactions, and how they are frequently exacerbated within self-reinforcing dynamic systems 3.) Investigate the constraints and vulnerabilities of evolved behavioural and cognitive control systems which generate aversive states of mood and anxiety and frequently become inflexible. Several conclusions are drawn in the final chapter which indicate some shifts in assumptions are likely needed to advance explanation and prediction in mood and anxiety disorders across scientific disciplines.