  Observables of quantum systems can posses either a discrete or a continuous
spectrum. For example, upon measurements of the photon number of a light state,
discrete outcomes will result whereas measurements of the light's quadrature
amplitudes result in continuous outcomes. If one uses the continuous degree of
freedom of a quantum system either for encoding, processing or detecting
information, one enters the field of continuous variable (CV) quantum
information processing. In this paper we review the basic principles of CV
quantum information processing with main focus on recent developments in the
field. We will be addressing the three main stages of a quantum informational
system; the preparation stage where quantum information is encoded into CVs of
coherent states and single photon states, the processing stage where CV
information is manipulated to carry out a specified protocol and a detection
stage where CV information is measured using homodyne detection or photon
counting.
