An inherent feature of parallel solid phase synthesis is the need to handle a large number of reaction vessels at the same time. Consequently, in order to make demanding synthetic tasks manageable, two categories of synthesizers, manual and automated, have been designed and produced. The main feature of a manual synthesizer is the integration of reaction vessels and common steps during synthesis. Reaction vessels are combined into so-called reaction blocks that enable performing specific operations (e.g., washing resin beads, adding common reagents, incubation) in all integrated reaction vessels at the same time. An automated synthesizer offers full automation of the entire synthetic process. The reaction vessels can be controlled on an individual basis and independent protocols can be performed in different vessels. Semiautomatic instruments feature integration and automation of the most commonly occurring steps. Even though full automation brings numerous advantages, the throughput of “manual” laboratories does not need to suffer. Without any expensive automated devices, production may still reach a thousand compounds per day.