Reducing Boolean Networks with Backward Boolean Equivalence -- Abstraction of Markov Population Dynamics via Generative Adversarial Nets -- Greening R. Thomas' Framework with Environment Variables: a Divide and Conquer Approach -- Automated inference of production rules for glycans -- Compiling Elementary Mathematical Functions into Finite Chemical Reaction Networks via a Polynomialization Algorithm for ODEs -- Interpretable exact linear reductions via positivity -- Explainable artificial neural network for recurrent venous thromboembolism based on plasma proteomics -- Neural networks to predict survival from RNA-seq data in oncology -- Microbial Community Decision Making Models in Batchand Chemostat Cultures.-Learning Boolean controls in regulated metabolic networks: a case-study -- Population design for synthetic gene circuits -- Nonlinear pattern matching in rule-based modeling languages -- Protein noise and distribution in a two-stage gene-expression model extended by an mRNA inactivation loop -- Aeon 2021: Bifurcation Decision Trees in Boolean Networks -- LNetReduce: tool for reducing linear dynamic networks with separated time scales -- ppsim: A software package for efficiently simulating and visualizing population protocols -- Web-based Structural Identifiability Analyzer BioFVM-X: An MPI+OpenMP 3-D Simulator for Biological Systems.

This book constitutes the refereed proceedings of the 19th International Conference on Computational Methods in Systems Biology, CMSB 2021, held in Bordeaux, France, September 22-24, 2021.* The 13 full papers and 5 tool papers were carefully reviewed and selected from 32 submissions. The topics of interest include biological process modelling; biological system model verification, validation, analysis, and simulation; high-performance computational systems biology; model inference from experimental data; multi-scale modeling and analysis methods; computational approaches for synthetic biology; machine learning and data-driven approaches; microbial ecology modelling and analysis; methods and protocols for populations and their variability; models, applications, and case studies in systems and synthetic biology. The chapters "Microbial Community Decision Making Models in Batch", "Population design for synthetic gene circuits", "BioFVM-X: An MPI+OpenMP 3-D Simulator for Biological Systems" are published open access under a CC BY license (Creative Commons Attribution 4.0 International License). * The conference was held in a hybrid mode due to the COVID-19 pandemic.