Abstract: A warehousing system comprises an array of storage bins arranged in vertical tiers with the tiers arranged in rows having access aisles extending along the rows. A mobile vertical life moves along the ends of the aisles and carries thereon a mobile transfer vehicle which can be elevated by the mobile vertical lift to any desired storage level and discharged therefrom onto rails extending along each storage level of each access aisle. The self-powered mobile transfer vehicle includes forks for transferring loads between the vehicle and a storage bin. At least one of the transfer vehicles in the system is a tier picking vehicle including a vacuum operated picking head mounted to be lowered and raised between the picking vehicle and a make-up transfer vehicle below the picking vehicle.