(Sama teksti on hieman laajempana väitöskirjani luvussa 3.1.2.)
As a scientific endeavour, the psychology of religion is almost as old as psychology more generally. Almost all of the major names in early psychology discussed religion and dedicated books to it (see, for example, Freud 1913; James 1902; Wundt 1906). In the 1930s, however, the tide turned and religion practically disappeared from the psychological research literature (Holm 1997, 99; Laitila 2006, 81–83; Loewenthal 2000, 7–9; Richards 2012, 871–872; Spilka 2012, 928–929; Wulff 1997, 185–186). The only exceptions were social and personality psychologists, such as Gordon Allport (see, for example, 1950), who were engaged in the measurement of religious beliefs and attitudes (Richards 2012, 871; Spilka 2012, 929). Apart from their efforts, the psychology of religion was mostly sustained by theologians and religious studies scholars (Holm 1997, 99; Spilka 2012, 929; Wulff 1997, 186).
After several decades of neglect, religion started to make a comeback in psychology (Holm 1997, 99; Loewenthal, 2000, 9–11; Richards 2012, 871–872). However, in Europe in particular, the psychology of religion continued to be located mainly in schools of theology, and not in those of psychology or social psychology. As a result, the developments in the latter disciplines have affected the psychology of religion only in a limited manner (Laitila 2006, 80 & 96; Stausberg 2008, 310; Wulff 1991, 31). This, in turn, has led scholars such as David M. Wulff (1991, 31) to call for a closer association between the psychology of religion and other branches of psychology.
Psychological studies on religion have largely concentrated on (especially North American) Christianity and adopted an individual differences approach to the topic (Abu-Raiya 2017, 546; 2013, 681; Herriott 2007, 48; Loewenthal 2007, 9; Widdicombe 2011, 468). Most research efforts have been devoted to designing measures of religiosity and correlating them with measures of personality, attitudes, and well-being (Anderson 2015, 180; Batson, Schoenrade & Ventis 1993, 181; Connolly 1999, 160; Hood 2013, 87; Laitila 2006, 94; Widdicombe 2011, 468).
Like psychology more generally, the psychology of religion is divided into a number of subdisciplines such as the developmental psychology of religion and the neuropsychology of religion. The social psychology of religion is a further subdiscipline that has become increasingly relevant in our time of increasing irreligion and religious conflict.
In recent decades and due to the globalisation of psychology, non-Western authors have increasingly attempted to develop psychologies that incorporate their cultural (and often religious) heritage. The resulting psychologies (for example, ‘Islamic psychology’) have an uneasy relationship with mainstream psychology (Richards 2012, 877). ‘Islamic psychology’ as a normative endeavour is conducted with a personal religious commitment to Islam. Islamic religiosity is not necessarily the topic of study here, but rather its starting point; research in Islamic psychology most often focuses on mental health and counselling, but it is guided by Islamic morality and grounded in Islamic religious sources (see, for example, Ashy 1999; Kaplick & Skinner 2017; Şahin 2013; Skinner 2018, 2010). In contrast to Islamic psychology, the psychology of religion – including that of Islam – strives to be non-normative and to refrain from making religious truth claims. A psychologist of religion seeks to understand the role of religion in the lives of his or her informants, while at the same time remaining neutral with regard to its truth value (Hood, Hill & Spilka 2009, 3–5). Somewhat pointedly, one could argue that the main difference between the two psychologies is in their preferred direction of analysis: Islamic psychology uses Islamic theories and concepts to analyse the human mind and behaviour, whereas the psychology of religion analyses Muslim (or other) religiosity with reference to general theories of mental functioning.
 Reviews typically point to the USA at the turn of the 20th century as the birthplace of the scientific psychology of religion (see, for example, Kato 2016, 71; Laitila 2006, 80–83; Richards 2012; Spilka 2012; Suojanen 2000, 92–93).
 It has been estimated that between 1950 and 1974, social psychologists conducted approximately 70 per cent of the published research in the psychology of religion (Connolly 1999, 160; see also Laitila, 2006, 94).
 Loewenthal (2000, 10) has reported that before 1993, an average undergraduate textbook on personality or social psychology contained zero references to religion. Since then, the average number of references has increased to four.
 See Tapper (1995) for a related discussion on ‘Islamic anthropology’ and ‘anthropology of Islam’.