Valve Hammer Editor (sometimes shortened to "VHE" or "Hammer") is the official editor for GoldSrc and Source mapping. VHE was originally distributed under the name WorldCraft. VHE is now split into two versions; VHE 3.x for GoldSrc mapping, and VHE 4.x for Source mapping.
While VHE is the official editor, there are some alternatives that provide greater capabilities, each with their own pros and cons. Some alternatives to VHE for GoldSrc mapping are the Sledge Editor and the J.A.C.K. editor.