After discovery of the first direct renin inhibitor, aliskiren, which blocks the renin-angiotensin-aldosterone system in the first rate limiting step, in addition to angiotensin-converting enzymes (ACE) and angiotensin-receptor blockers (ARB), renin has become an important target nowadays. The scope of this review is to give a detailed information regarding renin which has an important regulatory function in the body. It is crucial to understand renin and related structures in order to understand its functions in the organ systems. It is for sure that the ongoing trials will enlighten us more regarding the beneficial effects of renin inhibition in terms of morbidity and mortality.