Image-guided wide local excision has moved away from using wires to localise tumours. Instead, implantable devices are now commonly used to localise impalpable cancers prior to surgery. Magseed® has been used in over 300,000 patients and is established in more countries than any of the other wire-free markers. Magseeds® can be deployed any time prior to surgery and do not degrade or migrate. The learning curve is demonstrably short both for radiologists and surgeons. With high levels of both patient and doctor satisfaction and reduced deployment and operative time, Magseed® has been proven to be a reliable and safe localisation technique. This chapter will describe the technology, cover basic radiological and surgical techniques and more advanced strategies for using Magseeds®, illustrated with case discussions, and review relevant literature.