It was introduced by Carl Woese, a Professor in the
department of Microbiology, University of Illinois in
1990. This system is also named as three domain system
as in it organisms are classified into three domains,
i.e., Archaea, Bacteria and Eukarya.
It mainly used basic principles of five kingdom system,
but divides Monera into two domains Archaebacteria,
Eubacteria and other eukaryotes in third kingdom.
i. Archaea
Archaea domain includes prokaryotic organisms. These
are characterised by a monolayer core of lipids in the cell
membrane and distinct nucleotides in their 16 S RNA.
It contains a single kingdom called Archaebacteria.
Kingdom—Archaebacteria
This kingdom includes early prokaryotes, which live in
extreme conditions of the environment. Include
methanogens, halophiles and thermoacidophiles.
ii. Bacteria
that
The bacteria domain consists of typical prokaryotes
lack membrane covered cell organelles. These do not have
microchambers for separating various metabolic activities
It also has a single kingdom—Eubacteria.
Kingdom—Eubacteria
The members of this kingdom have peptidoglycan cell wall,
naked DNA in coiled form and glycogen food reserves.
The sap vacuole is not present and 70 S ribosomes are present.
The members of this kingdom are bacteria, mycoplasma,
Actinomycetes, rickettsiae, spirochaetes, cyanobacteria.
iii. Eukarya
The domain eukarya contains all the eukaryotes.

The four kingdoms of this domain are
(a) Protista
(b) Fungi
(c) Plantae
(d) Animalia