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Abstract: One objective of this research was to obtain a correlation that quantitatively predicts micrometer-sized aerosol particle deposition in the upper conducting airways (trachea to generation 3) of children. Experiments were conducted using steady inhalation air flow rates to measure the deposition of monodisperse particles with diameters of 3.5–5.5 micro-meter in replicas of the upper tracheobronchial airways of 11 children aged 2–8 years. The total deposition of particles was measured in each replica using gravimetry. Validation was performed by measuring deposition in five adult replicas and comparing with existing published data. Although there is considerable intersubject variability in our data, the empirical correlation of Chan & Lippmann (1980) was found to predict total deposition reasonably well in all of our adult and child replicas. A second goal of this study was to design an idealized pediatric central conducting airway model that mimics average total particle deposition in the airways of 4-8 year old children. Dimensions of the idealized model were selected based on analytical prediction of deposition in scaled versions of existing adult airway geometries. Validation experiments were then conducted using steady inhalation air flow rate to measure the deposition of monodisperse particles with mass median diameters (MMD) of 3.5, 4.5, 5 and 5.2 micro-meter in the idealized pediatric model. The total deposition of particles was measured using gravimetry. Experimental data confirmed that aerosol deposition in the idealized pediatric central conducting airway geometry was consistent with the average deposition previously measured in 10 realistic airway replicas for children 4-8 years old. Finally, this thesis describes in vitro measurements of the total pressure loss at varying flow rate through anatomically realistic conducting airway replicas of ten children, 4 to 8 years old, and five adults. Experimental results were compared with analytical predictions made using published airway resistance models. For the adult replicas, the model proposed by van Ertbruggen et al. (J. Appl. Physiol. 98:970-980,2005) most accurately predicted central conducting airway resistance for inspiratory flow rates ranging from 15 to 90 L/min. Models proposed by Pedley et al. (J. Respir. Physiol. 9:371-386,1970) and by Katz et al. (J. Biomechanics 44:1137-1143,2011) also provided reasonable estimates, but with a tendency to over predict measured pressure loss for both models. For child replicas, the Pedley and Katz models both provided good estimation of measured pressure loss at flow rates representative of resting tidal breathing, but under predicted measured values at high inspiratory flow rate (60 L/min). The van Ertbruggen model, developed based on flow simulations performed in an adult airway model, tended to under predict measured pressure loss through the child replicas across the range of flow rates studied (2 to 60 L/min). These results are intended to provide guidance for selection of analytical pressure loss models for use in predicting airway resistance and ventilation distribution in adults and children.