Molecular beam epitaxy of dilute-nitride materials has progressed a long way towards claiming its unique place as a key technology, which enables the development of new types of optoelectronics devices. This chapter begins by reviewing the technological particularities related to incorporation of nitrogen into III–V materials when using plasma-assisted molecular beam epitaxy. We then focus on describing the interplay between the growth parameters and nitrogen incorporation processes in dilute-nitride arsenides (III-N–As). Emphasis is laid on nitrogen-related growth kinetics that is accompanied by various bonding configurations and formation of several types of defects. An overview is provided also for dilute-nitride antimonides (III-N–Sb) and dilute-nitride phosphides (III-N–P). Finally, we review the growth optimisation and properties of several classes of dilute-nitride heterostructures for optoelectronics. These include uncooled long-wavelength laser diodes, SESAMs, VECSELs, enabling yellow emission by frequency doubling, and high-efficiency multijunction solar cells for concentrated photovoltaic systems.