Gateway cloning is a molecular biology technique that allows efficient transfer of DNA fragments between plasmids using proprietary enzyme mixes and recombination sequences called "Gateway att sites". It involves two recombination reactions: BP reaction to create an entry clone, and LR reaction to create an expression clone in 1 hour at room temperature with over 95% efficiency, avoiding the need for restriction enzymes, ligation, or subcloning. The system enables rapid shuttling of DNA between vectors for applications like protein expression and RNAi.