In criminal law, a conspiracy is an agreement between two or more persons to break the law at some time in the future. Criminal law in some countries or for some conspiracies may require that at least one overt act must also have been undertaken in furtherance of that agreement, to constitute an offense. There is no limit on the number participating in the conspiracy and, in most countries, no requirement that any steps have been taken to put the plan into effect (compare attempts which require proximity to the full offence). For the purposes of concurrence, the actus reus is a continuing one and parties may join the plot later and incur joint liability and conspiracy can be charged where the co-conspirators have been acquitted or cannot be traced. Finally, repentance by one or more parties does not affect liability but may reduce their sentence.

At common law, the crime of conspiracy was capable of infinite growth, able to accommodate any new situation and to criminalize it if the level of threat to society was sufficiently great. The courts were therefore acting in the role of the legislature to create new offences and, following the Law Commission Report No. 76 on "Reform of the Common Law", the Criminal Law Act 1977 produced a statutory offence and abolished all the common law varieties of conspiracy, except two:

Conspiracy or conspirator may refer to:

Crime is the breach of rules or laws for which some governing authority (via mechanisms such as legal systems) can ultimately prescribe a conviction. Crimes may also result in cautions, rehabilitation or be unenforced. Individual human societies may each define crime and crimes differently, in different localities (state, local, international), at different time stages of the so-called "crime", from planning, disclosure, supposedly intended, supposedly prepared, incomplete, complete or future proclaimed after the "crime".^{[citation needed]}

While every crime violates the law, not every violation of the law counts as a crime; for example: breaches of contract and of other civil law may rank as "offences" or as "infractions". Modern societies generally regard crimes as offences against the public or the state, as distinguished from torts (wrongs against private parties that can give rise to a civil cause of action).

When informal relationships and sanctions prove insufficient to establish and maintain a desired social order, a government or a state may impose more formalized or stricter systems of social control. With institutional and legal machinery at their disposal, agents of the State can compel populations to conform to codes and can opt to punish or attempt to reform those who do not conform.