  We study the lowest-mass eigenstates of $\phi^4_{1+1}$ theory with both odd
and even numbers of constituents. The calculation is carried out as a
diagonalization of the light-front Hamiltonian in a Fock-space representation.
In each Fock sector a fully symmetric polynomial basis is used to represent the
Fock wave function. Convergence is investigated with respect to the number of
basis polynomials in each sector and with respect to the number of sectors. The
dependence of the spectrum on the coupling strength is used to estimate the
critical coupling for the positive-mass-squared case. An apparent discrepancy
with equal-time calculations of the critical coupling is resolved by an
appropriate mass renormalization.
