The issues of interpersonal and group processes in long-term spacecrews from the perspectives of social and organizational psychology are considered here. A contrast between the Amundsen vs. Scott expeditions to the South Pole 90 yrs. ago highlights the importance of personnel selection and attention to interpersonal and group dynamics in expeditions to extreme and dangerous environments, such as long-term spaceflights today. Under the rubric of personnel selection, some further psychological "select-in" and "select-out" criteria are suggested, among them implicit measures of human motivation, intergroup attitudes ("implicit" and "explicit" measures of prejudice, social dominance orientation, and right-wing authoritarianism), attachment styles, and dispositional hardiness. The situational interview and the idea of "selection for teams," drawn from current advances in organizational psychology, are recommended for selecting members for future spacecrews. Under the rubrics of interpersonal and group processes, the social relations model is introduced as a technique for modeling and understanding interdependence among spacecrew members and partialling out variance in behavioral and perceptual data into actor/perceiver, partner/target, and relationship components. Group cohesion as a multidimensional construct is introduced, along with a consideration of the groupthink phenomenon and its controversial link to cohesion. Group composition issues are raised with examples concerning cultural heterogeneity and gender composition. Cultural value dimensions, especially power distance and individual-collectivism, should be taken into account at both societal and psychological levels in long-term space missions. Finally, intergroup processes and language issues in crews are addressed. The recategorization induction from the common ingroup identity model is recommended as a possible intervention for overcoming and inhibiting intergroup biases within spacecrews and between space- and groundcrews.