  This document provides detailed information on the status of Advanced and
Novel Accelerators techniques and describes the steps that need to be envisaged
for their implementation in future accelerators, in particular for high energy
physics applications. It complements the overview prepared for the update of
the European Strategy for particle physics, and provides a detailed description
of the field. The scientific priorities of the community are described for each
technique of acceleration able to achieve accelerating gradient in the
GeV~range or above. ALEGRO working group leaders have coordinated the
preparation of their working group contribution and contributed to editing the
documents. The preparation of this document was coordinated by the Advanced
LinEar collider study GROup, ALEGRO. The content was defined through
discussions at the ALEGRO workshop in Oxford UK, March 2018, and an advanced
draft was discussed during a one day meeting prior to the AAC workshop in
Breckenridge, CO, USA, August 2018. This document was submitted as an addendum
to the ALEGRO submission to the European Strategy for Particle Physics.
