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Wavelet basis functions are a natural tool for analyzing turbulent flowscontaining localized coherent structures of different spatial scales. Here,wavelets are used to study the onset and subsequent transition to fullydeveloped turbulence from a laminar state. Originally applied to neutral fluidturbulence, an iterative wavelet technique decomposes the field into coherentand incoherent contributions. In contrast to Fourier power spectra, finite timeLyapunov exponents (FTLE), and simple measures of intermittency such asnon-Gaussian statistics of field increments, the wavelet technique is found toprovide a quantitative measure for the onset of turbulence and to track thetransition to fully developed turbulence. The wavelet method makes noassumptions about the structure of the coherent current sheets or theunderlying plasma model. Temporal evolution of the coherent and incoherentwavelet fluctuations is found to be highly correlated with the magnetic fieldenergy and plasma thermal energy, respectively. The onset of turbulence isidentified with the rapid growth of a background of incoherent fluctuationsspreading across a range of scales and a corresponding drop in the coherentcomponents. This is suggestive of the interpretation of the coherent andincoherent wavelet fluctuations as measures of coherent structures (e.g.,current sheets) and dissipation, respectively. The ratio of the incoherent tocoherent fluctuations $R_{ic}$ is found to be fairly uniform across differentplasma models and provides an empirical threshold for turbulence onset. Thetechnique is illustrated through examples. First, it is applied to theKelvin--Helmholtz instability from different simulation models including fullykinetic, hybrid (kinetic ion/fluid electron), and Hall MHD simulations. Second,it is applied to the development of turbulence downstream of the bowshock in amagnetosphere simulation.

Wavelet Methods for Studying the Onset of Strong Plasma Turbulence