Background: Hyaluronic acid injections for treatment of osteoarthritis of the knee are a widely used yet highly controversial therapy. Many societal guidelines recommend against the use of such injections. Objective: This review aims to investigate efficacy of intra-articular hyaluronic acid injections for treatment of osteoarthritis of the knee. Conclusion: There are many factors impacting the efficacy of intra-articular hyaluronic acid injections. This can include source of hyaluronic acid, dosing regimen, molecular weight of the product, and patient characteristics. Overall, hyaluronic acid injections can be effective in reducing pain and improving physical function in patients with osteoarthritis of the knee. These injections may also prolong time between diagnosis and arthroplasty. Adverse events after injection are rare and can be product-related. Radiologic findings and severity of disease can be predictive of successful treatment outcomes. More consistent research will be necessary to overturn societal guideline recommendations to support treatment with intra-articular hyaluronic acid products.