Geckos have evolved one of the most versatile and effective adhesives known. The mechanism of dry adhesion in the millions of setae on the toes of geckos has been studied for over a century. This study provides the first direct experimental evidence that gecko setae adhere via van der Waals forces, rejecting the role of capillary adhesion. The toes of live Tokay geckos were highly hydrophobic and adhered equally well to both hydrophobic and hydrophilic surfaces. Adhesion of a single gecko seta was equally effective on hydrophobic and hydrophilic surfaces of a microelectromechanical systems (MEMS) force sensor. A van der Waals mechanism implies that the adhesive properties of gecko setae depend on the size and shape of the tips, not surface chemistry. Theory predicts that increasing the surface density of setae would enhance adhesive forces, suggesting a design principle for the repeated evolution of dry adhesive structures in geckos, anoles, skinks, and insects. The measured forces closely predict the size of Tokay gecko setae. Physical models of setal tips fabricated from two materials showed similar adhesion, supporting the van der Waals hypothesis. The study also rejects the hypothesis that capillary adhesion is necessary for gecko adhesion, as geckos adhere equally well to hydrophobic and hydrophilic surfaces. The hydrophobic nature of gecko setae supports the van der Waals hypothesis and reduces the role of capillary adhesion. The van der Waals model predicts the size of spatulae based on adhesive force measurements. The physical models of spatulae showed adhesion forces consistent with van der Waals forces. The study suggests that the evolution of adhesive structures in geckos and other animals is based on geometric principles rather than surface chemistry. The findings indicate that dry adhesive microstructures can be manufactured by mimicking natural structures, using simple geometric designs. The results support the van der Waals hypothesis for gecko adhesion and provide a foundation for the development of synthetic adhesives.Geckos have evolved one of the most versatile and effective adhesives known. The mechanism of dry adhesion in the millions of setae on the toes of geckos has been studied for over a century. This study provides the first direct experimental evidence that gecko setae adhere via van der Waals forces, rejecting the role of capillary adhesion. The toes of live Tokay geckos were highly hydrophobic and adhered equally well to both hydrophobic and hydrophilic surfaces. Adhesion of a single gecko seta was equally effective on hydrophobic and hydrophilic surfaces of a microelectromechanical systems (MEMS) force sensor. A van der Waals mechanism implies that the adhesive properties of gecko setae depend on the size and shape of the tips, not surface chemistry. Theory predicts that increasing the surface density of setae would enhance adhesive forces, suggesting a design principle for the repeated evolution of dry adhesive structures in geckos, anoles, skinks, and insects. The measured forces closely predict the size of Tokay gecko setae. Physical models of setal tips fabricated from two materials showed similar adhesion, supporting the van der Waals hypothesis. The study also rejects the hypothesis that capillary adhesion is necessary for gecko adhesion, as geckos adhere equally well to hydrophobic and hydrophilic surfaces. The hydrophobic nature of gecko setae supports the van der Waals hypothesis and reduces the role of capillary adhesion. The van der Waals model predicts the size of spatulae based on adhesive force measurements. The physical models of spatulae showed adhesion forces consistent with van der Waals forces. The study suggests that the evolution of adhesive structures in geckos and other animals is based on geometric principles rather than surface chemistry. The findings indicate that dry adhesive microstructures can be manufactured by mimicking natural structures, using simple geometric designs. The results support the van der Waals hypothesis for gecko adhesion and provide a foundation for the development of synthetic adhesives.