This report gives a summary of the discussions in the Working Group on Errors during the Fifth Advanced ICFA Beam Dynamics Workshop, held at Corpus Christi, TX, USA from 3 to 8 October 1991. The following sources of errors in circular and linear accelerators and storage rings were discussed: Linear coupling, static position errors, dynamic position errors, nonlinear multipole components, persistent currents in superconducting magnets, and power supply ripple. The findings of the working group are summarized in the conclusions.