This review discusses the molecular mechanisms of plant responses to copper (Cu), focusing on both deficiency and excess. Cu is an essential micronutrient for plant growth and development, playing a key role in various biochemical pathways, including photosynthesis, respiration, and antioxidant systems. Despite its importance, the physiological significance of Cu uptake and compartmentalization in plants has been underestimated. Cu deficiency is a widespread issue, particularly in alkaline or organic-rich soils, leading to severe nutritional disorders. In contrast, excessive Cu can inhibit photosynthesis and induce oxidative stress, affecting plant productivity and posing health risks through bioaccumulation in the food chain. Plants have evolved complex molecular mechanisms to regulate Cu uptake, transport, and homeostasis. This review provides a comprehensive overview of the diverse functions of Cu chelators, chaperones, and transporters involved in Cu homeostasis and their regulatory mechanisms in plant responses to varying Cu availability conditions. It highlights the need for further research to enhance understanding of the mechanisms regulating Cu deficiency or stress in plants, which will help improve Cu utilization efficiency and/or Cu tolerance in crops grown in alkaline or Cu-contaminated soils. Keywords: copper; deficiency and phytotoxicity; transporter; transcriptional regulation; homeostasis.This review discusses the molecular mechanisms of plant responses to copper (Cu), focusing on both deficiency and excess. Cu is an essential micronutrient for plant growth and development, playing a key role in various biochemical pathways, including photosynthesis, respiration, and antioxidant systems. Despite its importance, the physiological significance of Cu uptake and compartmentalization in plants has been underestimated. Cu deficiency is a widespread issue, particularly in alkaline or organic-rich soils, leading to severe nutritional disorders. In contrast, excessive Cu can inhibit photosynthesis and induce oxidative stress, affecting plant productivity and posing health risks through bioaccumulation in the food chain. Plants have evolved complex molecular mechanisms to regulate Cu uptake, transport, and homeostasis. This review provides a comprehensive overview of the diverse functions of Cu chelators, chaperones, and transporters involved in Cu homeostasis and their regulatory mechanisms in plant responses to varying Cu availability conditions. It highlights the need for further research to enhance understanding of the mechanisms regulating Cu deficiency or stress in plants, which will help improve Cu utilization efficiency and/or Cu tolerance in crops grown in alkaline or Cu-contaminated soils. Keywords: copper; deficiency and phytotoxicity; transporter; transcriptional regulation; homeostasis.