There are many suggested motives for spying that an individual may have. In general, espionage carries heavy penalties, with spies often being regarded as traitors, and so motivating factors must usually be quite large.
There have been various attempts to explain why people become spies. One common theory is summed up by the acronym "MICE", which stands for "Money, Ideology, Compromise or Coercion (depending on source), and Ego". Other explanations have stressed the role of disaffection and grudges, or of personal links.
For many spies, the primary motivating factor is the prospect of financial gain. Spies may simply seek to supplement whatever income they already receive, or may be driven to spy due to financial difficulties. Sometimes, these spies are detected due to extravagant spending of the money they receive. Aldrich Ames and John Anthony Walker are examples of spies who worked for money.
Ideology, patriotism, or religion
Sometimes, a person will become a spy simply because of their beliefs. These can include their political opinions, their national allegiences, or their cultural or religious beliefs. This was particularly true during the Cold War, when many spies were motivated by support for the ideological positions of either the Western world or the Communist bloc. Examples of spies with ideological motivations include Kim Philby and Klaus Fuchs (communist), Fritz Kolbe and Juan Pujol (anti-Nazi), Nathan Hale (pro-American independence), Harriet Tubman (anti-slavery), Ana Montes (pro-Cuban) and Jonathan Pollard (pro-Israeli).
Disaffection and grudges
On some occasions, a spy is motivated largely by personal, non-ideological hostility towards the country or organisation that they are spying on. This may stem from some real or imagined wrong — a person may, for example, betray secrets to the enemy if they feel that they have not been given sufficient recognition, or they have been treated badly. Liu Liankun, a general in the People's Republic of China, is believed to have begun spying for Taiwan after being falsely accused of corruption and therefore denied a promotion. Another case is that of Earl Edwin Pitts, who, in defence of his espionage, cited various instances of alleged poor treatment by his employer, the FBI.
A spy may also be motivated by personal connections and relationships. In some cases, secret information may be passed on due to a family connection, a friendship, a romantic link, or a sexual relationship. In particular, the spouses and friends of an active spy may sometimes be drawn into the spy's activities — an example is Rosario Ames, wife of Aldrich Ames. The tactic of seducing a potential source of information is also well-established — for example, Katrina Leung is accused of using this method to gain access to secret FBI counter-intelligence documents.
Self-importance or excitement
The role of ego and pride in motivating spies has occasionally been observed, but is often hard to demonstrate. In some situations, a person can be inticed to spy by the sense of importance or significance which it gives them — they cease to be simply a minor functionary, and are having a substantial impact. This motivation often involves the target gaining a sense of superiority over his or her colleagues, who he or she is outwitting. In rare cases, a spy may even be motivated by excitement, — is one of the few examples.
It is possible, although hard to observe and demonstrate, that excitement and thrills play a part in the decisions of some spies. This is particularly true if they are bored with their life. Excitement is seldom the primary motivation of a spy, but may be a contributing factor. One notable example of a spy motivated primarily by excitement, however, is Christopher Cooke, who claimed to be fascinated with espionage, and who told investigators that he specifically sought to involve himself in spycraft for that reason.
Not all spies enter into service willingly — sometimes, a person can be threatened into providing secret information to another country.
Threats of injury or death are the most direct form of coercion. For example, Mathilde Carré, a member of the French Resistance, was captured by the Nazis and threatened with torture unless she became a double agent. Threats can also be made against family or friends of the target — Svetlana Tumanova was told by the KGB that her family in the Soviet Union would be harmed if she did not co-operate, and Ronald Humphrey said that he had helped North Vietnam in order to obtain the release of his Vietnamese wife.
A more subtle form of coercion is blackmail, with a government threatening to release embarrassing information about a person's activities unless that person provides them with secret information. A wide range of material can be used for blackmail — extramarital affairs, homosexuality, and undiscovered crimes have all been used for this purpose. John Vassall and Alfred Redl, who were threatened with revelations about their homosexuality, are both example of this type of spy. Sometimes, traps of this sort may be laid especially to collect blackmail material — Vassal was almost certainly set up, as was Clayton Lonetree, who was blackmailed after an affair with a Soviet agent. William Sebold, a German-born American, was threatened by the Nazis with revelations that he lied in order to immigrate. Sebold, however, quickly betrayed the Nazis, indicating a major problem with the use of coercion — the target has no real loyalty to their blackmailers, and will turn on them when possible.