Infertility is defined as the clinical inability to achieve pregnancy despite regular and unprotected sexual intercourse for at least one year and constitutes an important public health problem worldwide. The male factor is the primary factor in approximately 20% of infertility cases and contributes to 30-40% of total infertility cases. A comprehensive evaluation of male infertility requires basic diagnostic methods such as semen analysis and analysis of sperm parameters. In case of abnormal findings, hormonal evaluation and further investigations are recommended. In recent years, a significant global decline in male fertility has been observed and a multifactorial aetiology for this decline has been demonstrated. Individual lifestyle factors such as environmental toxins, obesity, smoking and alcohol use are among the main factors that adversely affect sperm production and quality. In particular, exposure to endocrine disrupting chemicals, heavy metals and microscopic toxins adversely affects spermatogenesis and leads to serious decreases in semen quality. Experimental and epidemiological studies confirm the toxic effects of environmental exposure on spermatogenetic processes. This decrease in male fertility is due to the combined effects of biological, environmental and lifestyle factors, and it is of great importance to address these factors in detail and develop appropriate treatment and preventive strategies. In this chapter, the effects of factors that may adversely affect the male reproductive system on reproductive toxicity are comprehensively analysed and evaluated from various perspectives.