Many people have contributed to lmfit.

Matthew Newville wrote the original version and maintains the project.
Till Stensitzki wrote the improved estimates of confidence intervals, and
    contributed many tests, bug fixes, and documentation.
Daniel B. Allan wrote much of the high level Model code, and many
    improvements to the testing and documentation.
Antonino Ingargiola wrote much of the high level Model code and provided
    many bug fixes.
J. J. Helmus wrote the MINUT bounds for leastsq, originally in
    leastsqbounds.py, and ported to lmfit.
E. O. Le Bigot wrote the uncertainties package, a version of which is used
    by lmfit.
Michal Rawlik added plotting capabilities for Models.
A. R. J. Nelson added differential_evolution, and greatly improved the code
    in the docstrings.

Additional patches, bug fixes, and suggestions have come from Christoph
    Deil, Francois Boulogne, Thomas Caswell, Colin Brosseau, nmearl,
    Gustavo Pasquevich, Clemens Prescher, LiCode, and Ben Gamari.

The lmfit code obviously depends on, and owes a very large debt to the code
in scipy.optimize.  Several discussions on the scipy-user and lmfit mailing
lists have also led to improvements in this code.