Substance over form is an accounting principle used "to ensure that financial statements give a complete, relevant and accurate picture of transactions and events". If an entity practices the 'substance over form' concept, the financial statements will show the financial reality of the entity (economic substance), rather than the legal form of transactions (form)[1]. In accounting for business transactions and other events we measure and report the economic impact of an event instead of its legal form. Substance over form is critical for reliable financial reporting. It is particularly relevant in case of revenue recognition, sale and purchase agreements, etc.
Examples
A lease might not transfer ownership to the leasee but the leasee has to record the leased items as an asset if it intends to use it for major portion of its useful life or where the present value of lease payment is fairly equal to the fair value of the asset, etc. Although legally the leasee is not the owner, so the leased item is not his asset, but from the perspective of the underlying economics the leasee is entitled to the benefits embedded in the use of the item and hence it has to be recorded as an asset. A company is short of cash, so it sells its machinery to the bank and obtains it back on a lease. It is called sale and leaseback. Although the legal ownership has transferred but the underlying economics remain the same and hence under the substance over form principle the sale and subsequent leaseback are considered one transaction. If two companies swap their inventories they will not be allowed to record sales because not sales has occurred even if they have entered into valid enforceable contracts.