  We study the interlayer coherent incompressible phase in Trilayer Quantum
Hall systems (TLQH) at total filling factor $ \nu_{T}=1 $ from three
approaches:
  Mutual Composite Fermion (MCF), Composite Boson (CB) and wavefunction
approach.
  Just like in Bilayer Quantum Hall system, CB approach is superior than
  MCF approach in studying TLQH with broken symmetry. The Hall and Hall drag
resistivities are found to be quantized at $ h/e^{2} $. Two neutral gapless
modes with linear dispersion relations are identified and the ratio of the two
velocities is close to $ \sqrt{3} $.
  The novel excitation spectra are classified into two classes: Charge neutral
bosonic
  2-body bound states and Charge $ \pm 1 $ fermionic 3-body bound states.
  In general, there are two 2-body Kosterlize-Thouless (KT) transition
temperatures and one 3-body KT transition. The Charge $ \pm 1 $ 3-body
fermionic bound states may be the main dissipation source of transport
measurements.
  The broken symmetry in terms of $ SU(3) $ algebra is studied. The structure
of excitons and their flowing patterns are given. The coupling between the two
Goldstone modes may lead to the broadening in the zero-bias peak in the
interlayer correlated tunnelings of the TLQH. Several interesting features
unique to TLQH are outlined.
  Limitations of the CB approach are also pointed out.
