By the nineteenth century, root climbers and adhesive-tendril climbers were known to exhibit negative phototropism. Negative phototropism is shared by various plant species belonging to many taxonomic families and is considered to be an outcome of parallel evolution. Through negative phototropism, lianas search for supporting hosts; however, compared with positive phototropism, which occurs during germination, there is little research on the properties of negative phototropism. This chapter presents a technique for quantifying negative phototropism in root climbers and adhesive-tendril climbers, which involves casting light on one side of a liana shoot and measuring the coordinates of the shoot tip and the angle of curvature of the entire shoot relative to the gradient of the light conditions.