Crop wild relatives (CWRs) have high levels of genetic diversity compared to their domesticated descendants. Soybean (Glycine max) has over 20 species of CWRs, most of which are in secondary and tertiary gene pools. Glycine soja, hereafter ‘soja,’ is the only wild relative in the primary gene pool, i.e., species that readily cross with soybean. Soja has many advantageous traits that may be transferrable to soybean, including resistance to insect pests, with particularly strong sources of resistance to the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae). Soybean aphid has been a major soybean pest in the United States and Canada since 2000 and a longstanding pest in East Asia. This paper reviews the challenges of developing soybean with durable resistance to soybean aphid in light of multiple, virulent biotypes in North America and China. It also examines particular challenges in evaluating soja germplasm for soybean aphid resistance and resultant solutions to those challenges. Soja germplasm is widely available, but from our experience, the logistics associated with reliably procuring high-quality soja seed has posed the main challenge in working with this CWR. This review highlights soja accessions identified with strong resistance to soybean aphid and their genetic bases, and it discusses possible strategies for exploiting aphid-resistant soja accessions to improve soybean pest management.