“任意信托”与“法定信托”相对。当信托以信托关系成立的方式为依据，即可分为“任意信托”和“法定信托”。

任意信托是根据事人之间的自由意思表示而成立的信托称为任意信托，任意信托又称为自由信托或明示信托，主要指委托人、受托人、受益人自由自愿形成信托关系，而且这种自由自愿意思在信托契约中明确地表示出来，大部分信托业务都属于任意信托。法定信托是与任意信托相对应的一种信托形式，指由司法机关确定当事人之间的信托关系而成立的信托，信托的当事人之间原本并没有成立信托的意思，司法机关为了当事人的利益，根据实际情况和法律规定，判定当事人之间的关系为信托关系，当事人无论自己的意思如何，都要服从司法机关的判定。设立法定信托的目的主要是保护当事人的合法利益， 防止当事人财产被不法使用。例如遗产，赡养费用等。

“任意信托”的英文表达为：express trust，其又可以细分为完整的任意信托（Executed express trust）和将来有效的任意信托（Executory express trust）。

当信托形成时意思已经表达完整的，即为完整的任意信托；当信托形成后尚需信托设定者用某种行为加以补充的，即为将来有效的任意信托。

附任意信托的英文释义：An express trust is a trust created "in express terms, and usually in writing, as distinguished from one inferred by the law from the conduct or dealings of the parties."[1] Property is transferred by a person (called a trustor, settlor, or grantor) to a transferee (called the trustee), who holds the property for the benefit of one or more persons, called beneficiaries. The trustee may distribute the property, or the income from that property, to the beneficiaries. Express trusts are frequently used in common law jurisdictions as methods of wealth preservation or enhancement.

另：法定信托的的英文表达为statutory trust。其英文释义为：Statutory trust means an unincorporated association which: (1) Is created by a governing instrument under which property is or will be held, managed, administered, controlled, invested, reinvested and/or operated, or business or professional activities for profit are carried on or will be carried on, by a trustee or trustees or as otherwise provided in the governing instrument for the benefit of such person or persons as are or may become beneficial owners or as otherwise provided in the governing instrument, including but not limited to a trust of the type known at common law as a “business trust,” or “Massachusetts trust,” or a trust qualifying as a real estate investment trust under § 856 et seq. of the United States Internal Revenue Code of 1986 [26 U.S.C. § 856 et seq.], as amended, or under any successor provision, or a trust qualifying as a real estate mortgage investment conduit under § 860D of the United States Internal Revenue Code of 1986 [26 U.S.C. § 860D], as amended, or under any successor provision; and (2) Files a certificate of trust pursuant to § 3810 of this title.

e.g. The Bill seeks to establish a statutory trust fund for providing financial support to educational, research and other projects and activities relating to environmental and conservation matters.

条例草案旨在设立一项法定信托基金，以资助与环境保育事宜有关的教育、研究及其他计划和活动。