Development in plants is a continuous process during which new tissues and organs are formed all along its life cycle. Development involves the coordination of both time and space of complex cellular processes such as proliferation, expansion and differentiation following endogenous programmes and in response to environmental signals. Since their discovery in 2002, plant microRNAs (miRNAs), a class of small single-stranded regulatory ribonucleic acids (RNAs) have emerged as important nodes in regulatory networks controlling plant development. For instance, miRNAs play important roles for cell fate determination during the patterning of organs and contribute to the regulation of their growth. In addition, miRNAs integrate different signals to regulate the life cycle of plants. Finally, miRNAs appear as molecular links between environmental signals and plant development and may constitute levers to modify plant development in crops.