Heavy Quarks at Threshold: Recent Developments

Recent developments in the treatment of a system of heavy quarks close to their production threshold are discussed. Particular emphasis is put on the next-to-next-to-next-to-leading order (N$^3$LO) corrections to the energy levels and the wave function and their effect on the cross section $\sigma(e^+e^-\to t\bar{t})$. Furthermore, the resummation of logarithmic corrections within the framework of potential non-relativistic QCD (pNRQCD) are considered.