  We describe a method to estimate the mass distribution of a gravitational
lens and the position of the sources from combined strong and weak lensing
data. The algorithm combines weak and strong lensing data in a unified way
producing a solution which is valid in both the weak and strong lensing
regimes. We study how the result depends on the relative weighting of the weak
and strong lensing data and on choice of basis to represent the mass
distribution. We find that combining weak and strong lensing information has
two major advantages: it eliminates the need for priors and/or regularization
schemes for the intrinsic size of the background galaxies (this assumption was
needed in previous strong lensing algorithms) and it corrects for biases in the
recovered mass in the outer regions where the strong lensing data is less
sensitive. The code is implemented into a software package called WSLAP (Weak &
Strong Lensing Analysis Package) which is publicly available at
http://darwin.cfa.harvard.edu/SLAP/
