  Notifications provide a unique mechanism for increasing the effectiveness of
real-time information delivery systems. However, notifications that demand
users' attention at inopportune moments are more likely to have adverse effects
and might become a cause of potential disruption rather than proving beneficial
to users. In order to address these challenges a variety of intelligent
notification mechanisms based on monitoring and learning users' behavior have
been proposed. The goal of such mechanisms is maximizing users' receptivity to
the delivered information by automatically inferring the right time and the
right context for sending a certain type of information.
  This article provides an overview of the current state of the art in the area
of intelligent notification mechanisms that relies on the awareness of users'
context and preferences. More specifically, we first present a survey of
studies focusing on understanding and modeling users' interruptibility and
receptivity to notifications from desktops and mobile devices. Then, we discuss
the existing challenges and opportunities in developing mechanisms for
intelligent notification systems in a variety of application scenarios.
