This chapter examines Junayd’s fundamental concepts that constitute his system of thought. Of particular interest here are his doctrines of oneness (tawḥīd), the primordial covenant (mīthāq), sobriety (ṣaḥw), annihilation (fanā) and abiding in God (baqāʾ). Discussions of these key concepts must also consider Junayd’s attempts to establish a consensual view of Sufi piety, in which differences between individual tendencies are purposefully blurred. His doctrine of fanāʾ, for instance, reflects various early approaches towards this state, and serves as a fascinating example of Junayd’s strategy to integrate one of the most controversial terms of early Sufism into a full-fledged cosmological-mystical system that embeds communal-ethical dimensions.