There are some areas of mathematics which baffle and perplex even the most hard-working and conscientious of students. Concepts which, when they appear on the horizon, cause teachers to shiver in terror at the thought of having to descend into a hole from which there appears no means of escape. What if I told you that the difficulty, challenge and strife they cause were the very same features which make them central to our mathematical development? In knowing what these concepts are, understanding the properties they share and developing an awareness of the strategies we must employ, we create the opportunity to address them in real-time and to support our pupils in traversing even the most treacherous of thresholds. There is light at the end of the tunnel but first we'll need to spend some time thinking deeply about threshold concepts...