Phenotypic plasticity is the potential of a genotype to form different phenotypes in contrasting environments. Phenotypic plasticity is always present among plant leaves due to modularity of design such that individual leaves can acclimate to their own environment. Plasticity differs among genotypes, populations, and species and as the result plants vary in their capacity to reach the optimum phenotype and maximise fitness under different environmental conditions. Owing to high energy and carbon costs of plasticity, being most plastic does not always guarantee the maximum fitness, and the benefit of a given plastic modification depends on the rate of environmental variability, extent of plasticity, potential reversibility, and leaf longevity. There are extensive variations in the degree of plasticity, rate of plastic changes, and reversibility of different leaf chemical, physiological, and structural leaf traits. In particular, leaf chemical and physiological traits change faster and more reversibly than structural traits. Leaf photosynthetic plasticity is often structural, determined during leaf development, and therefore, largely irreversible, especially the light-dependent plasticity. Plant adaptability to the environment is driven by plasticity and ecotypic adaptation to environmental conditions and species from different plant functional types largely vary in the share of different adaptability components along resource availability gradients. Globally, the plastic component is expected to be greater in species from high resource habitats with higher leaf metabolic activity and leaf turnover and less in species from low resource habitats with opposite suite of leaf traits. Plant functional types with persistent leaves and low leaf metabolic activity rely primarily on high constitutive tolerance to survive adverse environmental conditions, whereas plant functional types with short leaf lifespan and high leaf metabolic activity survive adverse conditions by plastic trait modifications or avoidance (ephemerals). Future work should focus on understanding the global variation in leaf plasticity as driven by plant metabolic activity and rate of regulation of transcriptome and epigenome level changes.