  This is an introduction to the algebras $A\subset B(H)$ that the bounded
linear operators $T:H\to H$ can form, once a complex Hilbert space $H$ is
given. Motivated by quantum mechanics, we are mostly interested in the von
Neumann algebras, which are stable under taking adjoints, $T\to T^*$, and
weakly closed. When the algebra has a trace $tr:A\to\mathbb C$, we can think of
it as being of the form $A=L^\infty(X)$, with $X$ being a quantum measured
space, and of particular interest is the free case, where the center of the
algebra is $Z(A)=\mathbb C$. Following Murray, von Neumann, Connes, Jones,
Voiculescu, Woronowicz, we discuss here the basic properties of such algebras
$A$, and how to do algebra, geometry, analysis and probability on the
underlying quantum spaces $X$.
