  This introductory review discusses the main problems facing the attempt to
build quantum information processing systems (like quantum computers) from
spin-based qubits. We emphasize 'bottom-up' attempts using methods from
chemistry. The essentials of quantum computing are explained, along with a
description of the qubits and their interactions in terms of physical spin
qubits. The main problem to be overcome is decoherence - how this works is
described, along with ways to suppress contributions from spin bath and
oscillator bath environments, and from dipolar interactions. Finally we discuss
various strategies for making chemistry-based spin qubits, using both magnetic
molecules and magnetic ions.
