The breeding of cucumber (Cucumis sativus) has changed over the last few hundred years, from open-pollinated populations, to inbred lines, to gynoecious hybrids. Speed breeding, marker-assisted selection and more efficient field testing have also led to advances with this crop. Production of inbred lines using doubled haploids has further decreased the time required to develop cultivars. Breeding of watermelon (Citrullus lanatus) has likewise become more complex. Early cultivars were open-pollinated populations selected for useful traits. Later, cultivars were developed by self-pollination of selections from populations. The chapter looks at advances in the breeding of both cucumber and watermelon. It first considers cucumber and technologies such as speed breeding. The latter section on watermelon provides an overview of the increasing complexity of breeding this crop. Traditional transformation, tissue regeneration and CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) systems are discussed for both crops. Parthenocarpy in both cucurbits is also covered.