ESDU Struct 00.07.00 introduces a group of documents in the Structures Series that deal with the behaviour of beams of thin-walled open cross section under torsion. It defines the torsion and warping constants using the equations that relate the twist per unit length to the applied torque. The warping constant is required in those equations when the torque is calculated about the shear centre@ and is itself the sum of the primary and secondary warping constants. Expressions for those two contributions to the warping constant are given and an equation for calculating the warping constant when the torque is calculated about an arbitrary point is also provided. ESDU Struct 00.07.01 gives the torsion and secondary warping constant for an angle section with or without a bulb@ while ESDU Struct 00.07.04 and ESDU 77023 give the primary warping constant respectively for a Z-section with or without a bulb and for lipped and unlipped channel- and Z-sections.