For a basical introduction to interpolation meaning, check this:
http://lib-www.lanl.gov/numerical/bookcpdf/c3-3.pdfHere I collected a little bibliography on fitting curves (spline, interpolation, and so on):Brown, Saad,'Hybrid Krylov method for non linear systems of equations', Siam, Sci, STAT.Comput.11, 3 may 1990James, Webber, "Interest Rate Modelling" Wiley, 2000Vasicek, Gifford Fong, "Term Structure Modelling using Exponential Splines", Journal of Finance, 37; 2 may 1982Finally, if you're interested in zero curves and smoothest forward-rate interpolation, try this good paper by Ken Adams. If I'm not wrong it was just recommended sorry for double recommendation. Have a nice week end.