A brief review of experimental results of defects in dilute nitrides studied by various techniques reported so far in the literature is given. The emphasis is on experimental signatures of grown-in defects in Ga(In)NAs and Ga(Al)NP, which are expected to play important roles in device performance and in determining the success of this novel material system for applications in optoelectronics. The authors' recent results from optically detected magnetic resonance studies of grown-in intrinsic defects, i.e. AsGa antisite in Ga(In)NAs and Ga self-interstitials in Ga(Al,In)NP, are discussed in more detail, in an effort to provide detailed information on the chemical identification and the formation mechanism of the defects as well as to reveal their role in degrading the optical quality of the materials. The review aims not only to provide an overview of the present knowledge and understanding of defects in dilute nitrides, but also to stress the urgent need for concerted efforts to positively identify the most important defects that are harmful to device performance and to design strategies to suppress them during growth or to eliminate them by post-growth treatments.