R package to build and use B-splines for interpolation and regression. In case of regression, equality constraints as well as monotonicity requirement can be imposed. Moreover, knot positions (not only spline coefficients) can be part of optimized parameters too. User is provided with functions calculating spline values at arbitrary points. This functions can be differentiated to obtain B-splines calculating derivatives at any point. B-splines of this package can simultaneously operate on a series of curves sharing the same set of knots. ‘bspline’ is written with concern about computing performance that’s why the basis calculation is implemented in C++. The rest is implemented in R but without notable impact on computing speed.