Multidimensional Nuclear Magnetic Resonance Peak Fitting and Analysis R package fitnmr version 1.0 Tools for fitting and analyzing 1D-4D nuclear magnetic resonance spectra with analytical models of peak shapes and peak groups. The package reads spectra in 'NMRPipe' format, builds constrained parameter structures for chemical shifts, line widths, scalar couplings, volumes, and phases, and performs nonlinear least-squares optimization for iterative peak discovery or simultaneous fits across multiple spectra. It also provides methods for visualization, preprocessing, and kinetic analysis of 1D time-series data, including automated phase optimization, solvent suppression, time-domain correction for frequency shifts and line broadening, modeling spectra as linear combinations of two component spectra, and exponential rate fitting. Software Imports: minpack.lm, abind, Matrix, methods Suggests: knitr, rmarkdown, bookdown, gslnls Colin Smith <colin.smith@wesleyan.edu> Comprehensive R Archive Network (CRAN) Colin Smith [aut, cre] GPL-3 2026-03-19 application/tgz https://CRAN.R-project.org/package=fitnmr doi:10.32614/CRAN.package.fitnmr