This book constitutes the thoroughly referred post-workshop proceedings of the 4th
International Workshop on Hybrid Systems biology HSB 2015 held as part of the Madrid Meet
2015 event in Madrid Spain in September 2015. The volume presents 13 full papers together
with 2 abstracts of invited sessions from 18 submissions. The scope of the HSB workshop is the
general area of dynamical models in Biology with an emphasis on hybrid approaches - by no means
restricted to a narrow class of mathematical models - and taking advantage of techniques
developed separately in different areas.
