This is a mature Python library for global optimization of expensive black-box functions using Bayesian optimization. It provides the `BayesianOptimization` class that iteratively fits a Gaussian process regressor (via scikit-learn) to observed function evaluations and uses an acquisition function (Upper Confidence Bound, Expected Improvement, Probability of Improvement, or combined) to propose the next point to evaluate. The library supports constrained optimization, domain reduction, mixed continuous/integer/categorical parameters, asynchronous/parallel optimization, and state persistence. Its architecture is modular: acquisition functions are organized in a strategy pattern, parameters are polymorphic with a base class for custom types, constraints are modeled with separate GPs, and domain reduction is implemented as a transformer. The core algorithm is well-tested and documented, with examples ranging from toy functions to hyperparameter tuning. It is not a research notebook collection or data pipeline; it is a production-grade library intended for integration into optimization workflows.