  Engineered living materials (ELMs) are the most relevant contemporary
revolution in materials science and engineering. These ELMs aim to outperform
current examples of "smart", active or multifunctional materials, enabling
countless industrial and societal applications. The "living" materials
facilitate unique properties, including autonomy, intelligent responses,
self-repair, and even self-replication. Within this dawning field, most reviews
and documents have divided ELMs into biological ELMs, which are solely made of
cells, and hybrid living materials, which consist of abiotic chassis and living
cells. Considering that the most relevant feature of living material is that
they are made of (or include) living cell colonies and microorganisms, we
consider that ELMs should be classified and presented differently, more related
to life taxonomies than materials science disciplines. Towards solving the
current need for the classification of ELMs, this study presents the first
complete proposal of taxonomy for these ELMs. Here, life taxonomies and
materials classifications are hybridized hierarchically. Once the proposed
taxonomy is explained, its applicability is illustrated by classifying several
examples of biological ELMs and hybrid living materials, and its utility for
guiding research in this field is analyzed. Finally, possible modifications and
improvements are discussed, and a call for collaboration is launched for
progressing in this complex and multidisciplinary field.
