The revenue recognition principle is a cornerstone of accrual accounting together with the matching principle. They both determine the accounting period in which revenues and expenses are recognized. According to the principle, revenues are recognized when they are realized or realizable, and are earned (usually when goods are transferred or services rendered), no matter when cash is received.
There are some exceptions to this general rule of revenue recognition. In case of contracts like construction work, which take long time, say 2-3 years to complete, proportionate amount of revenue, based on the part of contract completed by the end of the period is treated as realised. Similarly, when goods are sold on hire purchase, the amount collected in installments is treated as realised.