The parameter of an pure AR(p) model can be estimated by OLS. Estimation of MA(q) or ARMA(p,q) models (with q>1) are non linear. [web:reg] ARMA Add-In estimates this models using the Levenberg-Marquardt algorithm. The derivates, which are needed for the estimation and the covariance matrix, are computed with numeric finite difference methods. After estimation the Add-In displays the coefficient results (including std.error, t-statistic, p-value), summary statistics (R², Adjusted R², Standard Error of Regression, sum of squared residuals, log likelihood, Durbin Watson, Akaike information criteria (AIC), Schwarz criteria (SIC), inverted MA/AR roots, Impulse response function as well as forecast evolution.