The technical study of Pieter Brueghel the Younger's replicas after his father has resulted in a deep understanding of his studio practice and copying process. This paper summarises the major findings, including the type and preparation of his panel supports, the materials, function and style of his underdrawings and the systematic build-up of his paint layers using identical reserves for copies of the same composition. Brueghel's design transfer technique - using pounced cartoons - is positively identified in one painting using infrared reflectography and inferred in his other copies through the use of reconstructions and overlaying tracings of multiple copies of the same compositions. That several hands contributed to the production is shown through stylistic analysis. Most of the signed paintings, however, seem to betray the work of a single hand at both the underdrawing and painting stages. This hand is likely to be that of the master himself. Finally, evidence from Pieter Bruegel the Elder's original paintings, reconsidered in the context of the technical examination of the copies, suggests that the great master himself had recourse to pounced cartoons for the transfer of certain of his compositions to panel.