Part I On Some of Sergey’s Works.- Working with Sergey Naboko on Boundary Triples.- Operator-Valued Nevanlinna–Herglotz Functions, Trace Ideals, and Sergey Naboko’s Contributions.- Mathematical Heritage of Sergey Naboko: Functional Models of Non-Self-Adjoint Operators.- On Crossroads of Spectral Theory with Sergey Naboko.- Sergey Naboko’s Legacy on the Spectral Theory of Jacobi Operators.- On theWork by Serguei Naboko on the Similarity to Unitary and Selfadjoint Operators.- Part II Research Contributions.- Functional Models of Symmetric and Selfadjoint Operators.- Schrödinger Operators with δ-potentials Supported on Unbounded Lipschitz Hypersurfaces.- Improved Lieb–Thirring Type Inequalities for Non-selfadjoint Schrödinger Operators.- Ballistic Transport in Periodic and Random Media.- On the Spectral Theory of Systems of First Order Equations with Periodic Distributional Coefficients.- Asymptotic Analysis of Operator Families and Applications to Resonant Media.- On the Number and Sums of Eigenvalues of Schrödinger-type Operators with Degenerate Kinetic Energy.- Gap Labelling for Discrete One-Dimensional Ergodic Schrödinger Operators.- Degenerate Elliptic Operators and Kato’s Inequality.- Generalized Indefinite Strings with Purely Discrete Spectrum.- Soliton Asymptotics for the KdV Shock Problem of Low Regularity.- Realizations of Meromorphic Functions of Bounded Type.- Spectral Transition Model with the General Contact Interaction.- Weyl’s Law under Minimal Assumptions.- Weyl–Titchmarsh M-Functions for ϕ-Periodic Sturm–Liouville Operators in Terms of Green’s Functions.- On Discrete Spectra of Bergman–Toeplitz Operators with Harmonic Symbols.- One Dimensional Discrete Schrödinger Operators with Resonant Embedded Eigenvalues.- On the Invariance Principle for a Characteristic Function.- A Trace Formula and Classical Solutions to the KdV Equation.- Semiclassical Analysis in the Limit Circle Case.