Dispersion engineering in silicon nitride (Si X N Y ) waveguides is investigated through the optimization of the waveguide transversal dimensions and refractive indices in a multi-cladding arrangement. Ultra-flat dispersion of -84.0 ± 0.5 ps/nm/km between 1700 and 2440 nm and 1.5 ± 3 ps/nm/km between 1670 and 2500 nm is numerically demonstrated. It is shown that typical refractive index fluctuations as well as dimension fluctuations during the fabrication of the Si X N Y waveguides are a limitation for obtaining ultra-flat dispersion profiles. Single-and multi-cladding waveguides are fabricated and their dispersion profiles measured (over nearly 1000 nm) using a low-coherence frequency domain interferometric technique. By appropriate thickness optimization, the zero-dispersion wavelength is tuned over a large spectral range in both single-cladding waveguides and multi-cladding waveguides with small refractive index contrast (3 %). A flat dispersion profile with ± 3.2 ps/nm/km variation over 500 nm is obtained in a multi-cladding waveguide fabricated with a refractive index contrast of 37 %. Finally, we generate a nearly three-octave supercontinuum in this dispersion flattened multi-cladding Si X N Y waveguide.