Teachers' motivational processes and psychological functioning are fundamental not only for their health, but also for their actual job performance. However, a large body of research has emerged over the last two decades that points to secondary school teaching as one of the professions most affected, at both a national and international level, by stress, burnout, and other physical and psychological disorders. Conversely, in recent years, the levels of job satisfaction and teaching engagement in some developed countries, including Spain, have registered the lowest levels since 1990. Consequently, all these factors have also provoked an increase in teachers' sick leave and intention to quit their jobs. Faced with this worrying situation that secondary school teachers are immersed in, research that seeks solutions geared towards improving teachers' well-being and psychological functioning at work seems to be justified. To do this, the self-determination theory (SDT) postulates the existence of three basic psychological needs (BPN) -autonomy, competence and relatedness-, which, if satisfied, may facilitate self-determined motivation towards an activity, for example teaching. Simultaneously, SDT argues that self-determined motivation influences a set of affective, cognitive, and behavioral outcomes, which include teachers' psychological functioning or their teaching styles. In parallel, the social, physical and psychological benefits of regular physical activity have been empirically demonstrated at length in workers through different theoretical mechanisms. According to the tenets of SDT (Deci and Ryan, 1985), and considering the benefits of physical activity, the three general aims of the present doctoral thesis are the following: (1) To validate and adapt different questionnaires to Spanish and to the context of secondary school teachers with the aim of measuring their motivation for teaching, BPN satisfaction, interpersonal teaching style and burnout (studies 1, 2, 3 y 4); (2) To analyze motivational processes and the psychological functioning of secondary school teachers through a double variable- and person-centered approach (studies 5 y 6); (3) To design, implement, and assess the effects of a leisure-time physical activity intervention program with work colleagues with focus on improving the psychological functioning of secondary school teachers (study 7). To carry the aims out, 584 secondary school teachers (M = 45.05 ± 8.97, 56.5% females) belonging to 106 different secondary schools (74.4% state or public schools) from the Region of Aragon participated in the program. In addition, two samples of 106 secondary school teachers were collected (M = 45.50 ± 8.80, 41.5% females and M = 46.10 ± 8.81, 40.6% females) belonging to two public secondary schools from the city of Huesca. These were used for the intervention study (study 7) and also to address secondary aims of other studies (studies 2 and 4). The variables measured were BPN satisfaction, self-determined motivation, burnout, anxiety, depression, sleep quality, engagement, job satisfaction and teaching style. In addition, other sociodemographic variables such as gender, teaching experience or type of school, among others, were measured. As regards to the first aim, the first four studies show that the Motivation for Teaching Scale in Secondary Education (EME-ES), the Basic Psychological Needs at Work Scale (BPNWS-Sp), the Need-Supportive Teaching Style Scale (NSTSS) and the Burnout Clinical Subtype Questionnaire (BCSQ-12) are valid, reliable, and invariant scales with adequate psychometric properties, to assess these constructs in secondary school teachers. In addition, female teachers, state school teachers, and experienced teachers (i.e., > 16 years), are more likely to experience some burnout subtype. With regard to the second aim, this doctoral thesis demonstrates the importance of motivational processes for the correct performance of the teaching profession. First, the relevance of satisfying three BPNs in teachers is highlighted, to achieve self-determined motivation for teaching as well as to avoid controlled motivation and amotivation. In particular, it seems fundamental to satisfy the need for competence and the need for autonomy. Second, whereas autonomous motivation is essential for adequate teacher psychological functioning, and to implement more adaptive teaching styles, amotivation leads to an opposite pattern of outcomes. Regarding controlled motivation, although it may drive to adaptive outcomes such as engagement for teaching, it also leads to a higher risk of suffering burnout and adopting an ego climate-based teaching style. On the other hand, the present doctoral thesis (i.e., study 6) shows that Farber's burnout proposal and engagement for teaching do not represent two perfect endpoints of the same continuum. Of five identified profiles, three of them show the coexistence of frenetic burnout and engagement. In addition, teachers characterized by moderate-high levels of engagement show the most adaptive response pattern (physical and psychological). The opposite occurs with teachers characterized by high levels of underchallenged burnout and wornout burnout. However, it is important to note that if teachers, characterized by high levels of engagement, also experience high levels of frenetic burnout, they are more likely to suffer anxiety, depression, and poor sleep quality. As regards to the third aim, the intervention study shows that developing two leisure-time physical activity sessions of one hour, with work colleagues from the same school throughout one academic year, improves teachers' need for relatedness, their job satisfaction and their engagement factors of vigor and absorption. However, this 32-session physical activity program is not effective to improve any of the three subtypes of burnout or dedication. To conclude, this set of results denotes the need to design and implement teachers' need-supportive based strategies that lead to autonomous motivation, avoiding teachers' motivations originated by pressures -internal or external- or without regulation. Throughout the seven studies, different ideas based on the theory are provided so that the educational administration, school boards and the teachers themselves can take them into account and implement them with the aim of optimizing their motivational processes, their psychological functioning at work, and consequently, their teaching quality. In addition, these initiatives should be complemented with the practice of physical activity with work-colleagues, which seems to be an effective strategy for improving engagement in teaching and job satisfaction. Therefore, the educational administration should be responsible for designing, organizing, offering, and encouraging these physical activity programs, which should be adapted to the context of each school and to the particular needs of teachers., International PhD, Cum Laude