This special issue “Mathematical Methods and Modelling in Emerging Fields of Science and Engineering” of the Journal of Interdisciplinary Mathematics (JIM) is mainly a collection of the articles from the “4th International Conference on Mathematical Modelling, Applied Analysis and Computation-2021 (ICMMAAC-21)” organized by Department of Mathematics, JECRC University, Jaipur, India during 05-07 August, 2021. The conference covered crucial topics of applicable mathematics and computing. The role of mathematical methods and modelling in scientific and engineering discipline is very crucial. The mathematical methods and modelling play their role in almost all areas of science, engineering, finance and social science, providing mathematical models that simulate distinct phenomena and behaviors of all types. Mathematical modelling assists scientists and engineers to describe the nature of a broad range of phenomena and processes in scientific and engineering fields. By utilizing the numerical results, they allow the working professionals to predict the evolution of those processes without using costly and difficult experiments. This special issue is devoted to the recent investigations in modern problems of mathematical modelling of physical, biological, chemical and engineering processes, complex systems, numerical and analytical methods. The articles appearing in this special issue are of interest to researchers and students in areas of sciences and engineering.