This book presents the extensions to the quaternionic setting of some of the main approximation
results in complex analysis. It also includes the main inequalities regarding the behavior of
the derivatives of polynomials with quaternionic cofficients. With some few exceptions all the
material in this book belongs to recent research of the authors on the approximation of slice
regular functions of a quaternionic variable. The book is addressed to researchers in various
areas of mathematical analysis in particular hypercomplex analysis and approximation theory.
It is accessible to graduate students and suitable for graduate courses in the above framework.
