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(In)GaAsN alloys with a few percent N have shown significant promise for a wide range of applications. However, N incorporation degrades the optical and electronic properties of GaAsN, which has not been sufficiently accounted for by any theory. Thus, the objective of this dissertation is to develop an understanding of the formation of N-related extrinsic and intrinsic point defects and their influence on the electronic properties of InGaAsN alloys. The presence of extrinsic N-related point defect, Si-N complexes, is suggested by a decrease in carrier concentration, n, with increasing N-composition in GaAsN:Si films but not modulation-doped heterostructures. For GaAsN:Te (GaAsN:Si), n increases substantially (minimally) with rapid thermal annealing (RTA) T, suggesting a competition between annealing-induced Si-N complex formation and a reduced concentration of N-related traps. Since Si-N complex formation is enhanced for GaAsN:Si growth with the (2 x 4) reconstruction, which has limited group V sites for As-N exchange, the (Si-N)As interstitial pair is identified as the dominant Si-N complex. Finally, using modulation-doped GaAs(N)/AlGaAs heterostructures, neutral scatterers, likely N interstitials, were identified as the dominant source of carrier scattering in the absence of Si-N complexes. For intrinsic N-related defects, we compared GaAsN films before and after RTA. For as-grown GaAs1-xNx films, an onset of a metal-insulator transition (MIT) at a much higher n than that in GaAs is observed, accompanied by a shrinkage of the electron Bohr radius, aB, with increasing x. In addition, the T-dependence of n for T>150K suggests the presence of a N-induced electron trapping level below the GaAsN CB edge, accompanied by a persistent photoconductivity (PPC) effect. After RTA, a transition occurs in the low T transport mechanism from hopping to extended band conduction, the T-dependence of n is suppressed, and the PPC effect vanishes. Interestingly, NRA reveals an RTA-induced decrease in N interstitial fraction, fint; the corresponding signatures for the reduction in fint are also identified in Raman spectra. Thus, it is likely that N interstitials are responsible for the MIT, the aB shrinkage, the N-induced trapping level, and the PPC effect. Thus, N interstitials are the dominant form of intrinsic N defects in GaAsN.