  In this paper, we consider the Cauchy problem of the cubic nonlinear
Schr\"{o}dinger equation with derivative in $H^s(\R)$. This equation was known
to be the local well-posedness for $s\geq \frac12$ (Takaoka,1999),
ill-posedness for $s<\frac12$ (Biagioni and Linares, 2001, etc.) and global
well-posedness for $s>\frac12$ (I-team, 2002). In this paper, we show that it
is global well-posedness in $H^{1/2(\R)$. The main approach is the third
generation I-method combined with some additional resonant decomposition
technique. The resonant decomposition is applied to control the singularity
coming from the resonant interaction.
