  We present studies from the LHCb experiment leading to the measurement of the
weak phase {\phi}s. At first, flavor tagging is established by measuring the
B0s oscillation frequency \Deltams. Then, flavor tagging is used to perform a
measurement of the well known CKM angle sin 2{\beta} in B0 \rightarrow J/{\psi}
KS0, before we constrain {\phi}s through an amplitude analysis of B0s
\rightarrow J/{\psi} {\phi} decays. These studies use about 35 inverse pb of
data taken in 2010. In addition, we present the measurement of
B(B+\rightarrowJ/{\psi}{\pi}+)/B(B+\rightarrowJ/{\psi}K+) and the first
observation of B0s \rightarrowJ/{\psi}f2'(1525).
