The most commonly used definitions are those of the American Psychiatric Association and the World Health Organization. The American Psychiatric Association defines premature ejaculation as persistent or periodic minimal stimulation before, during, or shortly after penetration, and ejaculation before the individual’s will, causing significant distress or affecting the partnership. The World Health Organization defines premature ejaculation as the inability to delay ejaculation with full enjoyment of lovemaking, as evidenced by one of the following: ejaculation before or soon after the onset of intercourse (within 15 seconds); ejaculation occurs before reaching a full erection for sexual intercourse, the difficulty is not caused by a prolonged lack of sexual intercourse. The European Association of Urology (EAU) developed a new “Guidelines for the diagnosis and treatment of premature ejaculation” in 2015, which classifies premature ejaculation into four categories: 1. primary premature ejaculation; 2. secondary premature ejaculation; 3. natural variant premature ejaculation; 4. premature ejaculation-like ejaculatory dysfunction; the latter two are not strictly considered diseases because the intravaginal ejaculatory latency period (IELT) is within the normal range. Natural variant premature ejaculation manifests as irregular, non-continuous occurrence, within the normal fluctuation of sexual life, and occurs only occasionally, which may be related to the frequency of recent sexual intercourse, novelty to sexual partners and the environment of sexual intercourse; premature ejaculation-like ejaculatory dysfunction is subjectively described as having continuous or non-continuous occurrence of ejaculation earlier than expected, but the latency period is within the normal range and able to be prolonged, which may be related to the patient’s misperception. Primary premature ejaculation (PPE) is characterized by rapid ejaculation at the 1st intercourse; rapid ejaculation at almost every intercourse and with every sexual partner; and an ejaculatory latency of less than 2 minutes in most cases (90%). Secondary premature ejaculation (SPE) is characterized by: normal ejaculatory latency before the appearance of premature ejaculation; premature ejaculation may be caused by other conditions and may appear suddenly or gradually; the patient ejaculates quickly at some point; it may resolve or be cured with treatment of the primary condition.