In the field of logistics, picking or order preparation[1]​ is the process of collecting material by removing packaged units or sets from a higher packaging unit that contains more units than those removed.[2]​ In general, the process in which material is collected by opening a packaging unit.

It can be a picking of units when unitary products are extracted from a box or a picking of boxes when boxes are collected from a pallet or a container, also called packing.

Picking is a basic process in the preparation of orders in warehouses that greatly affects the productivity of the entire logistics chain"), since, in many cases, it is its bottleneck.

Normally, it is a labor-intensive process and its optimization and mechanization is one of the ways to improve the performance of companies' internal logistics chain. Its improvement involves, logically, eliminating the least productive parts of the process. The most unproductive part is usually related to the movement between the different locations where the picking process of the different products will be carried out.

To eliminate these displacements there are two normally divergent solutions.

The first option, grouped order service or "wave picking", bases its effectiveness on the statistical concept of optimal route; This route optimally covers (under the concept defined in the Chinese postman problem, never passing through the same place twice) the different product collection positions and begins to have relevance from a certain number of different positions to be traveled. Since the distance traveled between collection operations is inversely proportional to the number of order lines to be served in the batch, its effectiveness is directly proportional to the number of orders grouped for simultaneous service. This grouping is limited by the physical conditions for filling the collection containers, so several solutions appear to increase the number of grouped orders, to be applied depending on the rotation characteristics of the products.

They can basically be reduced to two:

Both procedures are not incompatible, but rather it must be possible to combine them in the same warehouse, since each one has a specific field of application depending on the rotation and volumetrics of the products. The big drawback of service pools in techniques is always the space required for the pools.