Tradecraft. A term popularized in the novels of John le Carré, but practiced by spies throughout history. Tradecraft includes a number of methodologies, ranging from chalk-marked dead drops, and honey traps, to wiretapping, losing a tail, and safe houses. Spies have to master their craft if they are to be effective in the job while evading ever-suspicious counterintelligence units.
One of the most fundamental needs for a spy is their legend, or a well-prepared but made-up or assumed identity, also known as a cover. Legends allow intelligence officers unique access into companies, ministries, and groups of interest where they can recruit agents, manipulate unwitting insiders, or observe, report, and take direct action themselves.