  Differential-difference equation
$\frac{d}{dx}t(n+1,x)=f(x,t(n,x),t(n+1,x),\frac{d}{dx}t(n,x))$ with unknown
$t(n,x)$ depending on continuous and discrete variables $x$ and $n$ is studied.
We call an equation of such kind Darboux integrable, if there exist two
functions (called integrals) $F$ and $I$ of a finite number of dynamical
variables such that $D_xF=0$ and $DI=I$, where $D_x$ is the operator of total
differentiation with respect to $x$, and $D$ is the shift operator:
$Dp(n)=p(n+1)$. It is proved that the integrals can be brought to some
canonical form. A method of construction of an explicit formula for general
solution to Darboux integrable chains is discussed and for a class of chains
such solutions are found.
