Individuals with Autism Spectrum Disorders (ASD) show pervasive abnormalities of attention. Suppositions have been made that atypical attention modulation may contribute to the development of socio-communicative deficits in ASD. Attention is theoretically organized into three functionally separate but interrelated networks: alerting, orienting, and executive. Atypical attention function in ASD has been shown for specific attention networks as well as visual (dorsal and ventral) networks using electroencephalography (EEG), functional magnetic resonance imaging (fMRI), and functional connectivity MRI (fcMRI) methodology. To date, no study has used resting state (RS) fcMRI and Posner's attention network theory to explore the organization and efficiency of the attention networks and their relationship with socio-communicative functioning in ASD. RS fcMRI detects low-frequency blood oxygenation level (BOLD) signal fluctuations and provides a measure of intrinsic network connectivity. A previous fMRI activation study in normal adults established a series of regions implicated in the function of each attention network. Using regions defined by this study, the present study used resting state (rs) fcMRI to assess attention network organization in a sample of 19 adolescents with ASD and 17 matched typically developing (TD) individuals. Imaging analyses explored connectivity within attention networks and between attention network regions, as well as between network representative seeds and the whole brain. In addition, the Modified Attention Network Test (m_ANT) was used in a subsample of these participants to examine network efficiency and modulation. Network and region specific fc indices and m_ANT scores for individual networks were then correlated with measures of functional connectivity and socio-communicative functioning, including the Social Communication Questionnaire (SCQ), Social Responsiveness Scale (SRS), Autism Diagnostic Observation Schedule (ADOS), and Autism Diagnostic Interview (ADI). It was predicted that in adolescents with ASD, functional connectivity would be reduced within each attentional network, but atypically increased across networks (reflecting reduced independence of attention networks) in comparison with TD adolescents. Additionally, it was expected that in comparison with their TD peers, ASD adolescents would demonstrate inefficient attention modulation. Finally, it was hypothesized that atypical connectivity and performance on the m_ANT would be associated with socio-communication symptom severity in the ASD group. Results showed no difference between groups in within and between network region connectivity (ps > .05). However, significant differences between groups were found between each network representative seed and various brain regions outside attentional networks (ps < .05). These differences were characterized by under-connectivity in the ASD group between the alerting network seed and cerebellum and somatosensory cortex, between the orienting network seed and parietal and somatosensory cortex, and between the executive network seed and superior parietal regions. Inverse effects of over-connectivity in the ASD group were also detected between the alerting network seed and parietal regions, as well and the orienting network seed and frontal, superior parietal, temporal, and cerebellar regions. M_ANT results showed differing patterns of network interactions in the ASD group compared to TD, as well as differences in response times during some task conditions. As a whole, the ASD group showed less efficient patterns of attention network function and interaction. Results of correlations between network scores on the m_ANT as well as between network fc-indices showed evidence of more domain general, less independent attention networks in the ASD compared to the TD group. No significant correlations were found in either the TD or ASD groups between network scores or fc-indices and the Socio- Communication Questionnaire or Social Responsiveness Scale. However, there were significant correlations in ASD between alerting and orienting network scores and the ADOS Social scores and ADOS Social and Communication combined scores. In addition executive network fc-indices showed correlations with ADOS Communication Scores. These positive correlations indicate greater ASD symptom severity with increased network inefficiency. According to results of this study, ASD appears characterized by inefficient attentional function at the neural and behavioral levels. These atypicalities are related to symptom severity with regards to socio-communicative functioning and serve as a basis for further research into treatment and etiology.