Phosphogypsum (PG) wastes, including solid-state PG and liquid-state PG leachate, are industrial byproducts generated during the production of phosphoric acid. It is of great concern due to the large-scale product accumulation and environmental and geological hazards. Harmless treatment and green chemical resource utilization techniques emerge to be the critical solutions for solving the PG waste problem. This review aims to comprehensively summarize the recent advances in harmless treatment, resource recovery, and valorization of PG wastes. The technique advancements regarding the harmless treatment, decontamination, and valorization of solid-state PG waste with different physical, chemical, thermal, and biological approaches are summarized. Additionally, the comprehensive physical chemistry mechanisms underneath the treatment and valorization strategies for PG leachate have also been discussed. For future work, the challenges and perspectives for resource utilization of solid-state PG and leachate are highlighted. With the systematic information on these aspects, we expect this review will serve as a guideline for the young generations working on PG waste treatment and resource recovery.