There is a constantly growing interest in nonlocal models based on functional differential equations, due to their importance in many areas of applied science. Their role is becoming increasingly significant, as they can be applied in order to allow us to account for phenomena such as memory effects, distributed dependence on parameters, and nonevolutionary behavior of a process that otherwise cannot be described adequately. Further progress in this field is also motivated by the needs of the theory itself, as it provides a useful framework allowing one to treat many distinct objects, previously studied separately, in a unified way.

The considerable generality is responsible for the complexity and diversity of properties. The possibility of coexistence of delays with advances, dependence of argument deviations on the state of a process, nonlinear boundary conditions, and the presence of singular terms makes the models very complicated and their behavior difficult to predict. Hence, the development of reasonably general methods for their effective treatment is a current challenge.

This special issue aims to attract research works on recent developments in functional differential equations in a broad sense, including their applications in science and engineering, with a particular emphasis on complex behavior of systems with nonlocal dependence on the state. Review papers describing the progress on particular topics are also welcome.

Potential topics include but are not limited to the following:

• Functional differential systems and boundary value problems in complex models
• Complex dynamics in systems with deviations
• Monotone systems and maximum principles
• Oscillations, stability, and asymptotic behavior
• Constructive analysis and approximation methods for complex systems
• Models based on equations with singularities
• Functional differential models in applied sciences
• Models with infinitely many variables, differential equations in abstract spaces, and discontinuous systems