Purpose: To evaluate the marginal leakage of three different types of bonding agents used with two posterior composites and a giomer, available commercially. Material and Methods: Class II box-only cavities were prepared on 90 mandibular first molars with margins extending 1 mm beyond the cementoenamel junction. The samples were divided into nine groups based on three different bonding agents, two different composites, and a giomer. Cavities were restored per the manufacturer’s description. Teeth were subjected to a thermocycling procedure (500×, 5°C to 55°C) and dye penetration by immersing in a 2% methylene blue solution (Merck Specialties) for 24 hours. The marginal adaptation was evaluated as a continuous margin at the gingival level under a stereomicroscope. The results were analyzed using the Kruskal-Wallis and Mann-Whitney U tests. Results: The results of the groups with the total-etch technique showed no statistical difference between the nanohybrid Filtek Z250 XT (3M ESPE) and fine hybrid SwissTEC composite (Coltène\Whaledent AG). The groups with the self-etch technique showed no statistical difference when used with either of the two composites. The acid-etch technique showed better marginal adaptation than the self-etch technique. When the giomer (Beautifil II, Shofu) was used with the total-etch technique, it showed better adaptation than when used with the self-etch technique but overall showed more marginal leakage than the composites. Conclusion: The total-etch technique provided better marginal adaptation for the composites and giomer compared to the self-etch technique. Clinical Significance: The demand for esthetic restorations continues to increase, and composite restorations are now considered the material of choice for Class II cavities. There are various concerns with composite restorations, one of them being good marginal adaptation to increase the life of the restoration. This study evaluated marginal leakage with the nanohybrid composite Filtek Z250 XT, fine hybrid composite SwissTEC, and a giomer when used with the total-etch technique and self-etch technique and reported satisfactory adaptation with the total-etch technique.