We mainly collect together in this chapter those techniques that have been used for producing atomic beams when the parent substance is a molecule and so has to be dissociated. This process is also sometimes known as ‘cracking’. In general these dissociated molecules are called radicals and in addition to the production of beams of atomic hydrogen, oxygen, nitrogen and the halogens we also include any other radicals that we are aware have been formed into a beam. Because of their extreme reactivity, the atomic state of substances that are normally molecular were sometimes referred to as ‘active’, so, for example, active nitrogen referred to atomic nitrogen. We begin the discussion with hydrogen which occupies several sections and follow it in Section 6.6 with oxygen, since similar techniques are involved. Nitrogen is probably the most dif-cult molecule to dissociate because of its high dissociation energy, but we consider it next in Section 6.7, because of its importance as the chief atmospheric constituent. The techniques for actually forming a beam of the halogens are not particularly difcult, but working with them is unpopular more because of the problems of handling them in vacuum systems than of forming an atomic beam. They are discussed in Section 6.8. Finally a short Section 6.9 covers beams of other radicals and an even shorter 6.10 exceptionally discusses one production of a molecular beam.