The Advisory Committee on Immunization Practices recommends that all health care personnel (HCP) be vaccinated annually against influenza. Vaccination of HCP can reduce influenza-related morbidity and mortality among both HCP and their patients. To estimate influenza vaccination coverage among HCP during the 2013-14 season, CDC analyzed results of an opt-in Internet panel survey of 1,882 HCP conducted during April 1-16, 2014. Overall, 75.2% of participating HCP reported receiving an influenza vaccination during the 2013-14 season, similar to the 72.0% coverage among participating HCP reported in the 2012-13 season. Coverage was highest among HCP working in hospitals (89.6%) and lowest among HCP working in long-term care (LTC) settings (63.0%). By occupation, coverage was highest among physicians (92.2%), nurses (90.5%), nurse practitioners and physician assistants (89.6%), pharmacists (85.7%), and "other clinical personnel" (87.4%) compared with assistants and aides (57.7%) and nonclinical personnel (e.g., administrators, clerical support workers, janitors, and food service workers) (68.6%). HCP working in settings where vaccination was required had higher coverage (97.8%) compared with HCP working in settings where influenza vaccination was not required but promoted (72.4%) or settings where there was no requirement or promotion of vaccination (47.9%). Among HCP without an employer requirement for vaccination, coverage was higher for HCP working in settings where vaccination was offered on-site at no cost for 1 day (61.6%) or multiple days (80.4%) compared with HCP working in settings not offering free on-site vaccination (49.0%). Comprehensive vaccination strategies that include making vaccine available at no cost at the workplace along with active promotion of vaccination might be needed to increase vaccination coverage among HCP and minimize the risk for influenza to HCP and their patients. The opt-in Internet panel survey was conducted for CDC by Abt Associates, Inc. (Cambridge, Massachusetts) during April 1-16, 2014, to provide estimates of influenza vaccination coverage among HCP during the 2013-14 influenza season. Two preexisting national opt-in Internet panels were used to recruit HCP for the survey. HCP were recruited through e-mails and messages on the panel websites and were eligible for the survey if they reported working in at least one of eight health care settings or reported any patient contact. Professional clinical HCP (physicians, nurse practitioners, physician assistants, nurses, dentists, pharmacists, allied health professionals, technicians, and technologists) were recruited from the current membership roster of Medscape, a medical website managed by WebMD Health Professional Network. Medscape's terms of service explicitly permit WebMD Professional Network to contact members about programming, including survey research; panelists receive an honorarium for completing surveys. HCP in other occupations (e.g., assistants, aides, administrators, clerical support workers, janitors, food service workers, and housekeepers) who met eligibility criterion were recruited for a health survey from general population Internet panels operated by or in partnership with Survey Sampling International (SSI) that provide panel members with online survey opportunities in exchange for nominal incentives. Among the 2,054 HCP who entered the two panel survey sites and had eligible responses to the screening questions, 1,949 (94.9%) completed the survey.§ Sixty-six respondents with completed surveys who reported working in "other health care settings" were excluded because examination of other survey responses indicated that they were either unlikely to have contact with patients or that their work setting was not one of the health care settings of interest for this analysis. One respondent was excluded because of missing data for the question used to determine vaccination status, leaving a final analytic sample of 1,882 HCP. Survey items included demographic characteristics, occupation type, work setting, self-reported influenza vaccination, and employer vaccination policies (vaccination requirements, vaccination availability at the workplace, and promotion of vaccination [including recognition, rewards, compensation, and free or subsidized vaccination]). Based on responses to the questionnaire, occupation type for HCP from both opt-in Internet panel sources were divided into seven groups for this analysis: physicians, nurse practitioners/physician assistants, nurses, pharmacists, assistants/aides, other clinical HCP, and nonclinical HCP. Work settings for HCP from both opt-in Internet panel sources were divided into four groups for this analysis: 1) hospitals, 2) ambulatory care/physician offices, 3) LTC settings, and 4) other clinical settings. Respondents could specify working in more than one work setting. Sampling weights were calculated based on each occupation type by age, sex, race/ethnicity, work setting, and census region to represent the U.S. population of HCP. Vaccination coverage estimates from opt-in Internet panel surveys completed for the 2010-11, 2011-12, 2012-13, and 2013-14 seasons were compared to assess trends over time. Similar methodology was used for all four influenza seasons, although Internet panels used to recruit both clinical and nonclinical HCP in 2010-11 differed from those used in subsequent years. Because the study sample was based on HCP from opt-in Internet panels rather than probability samples, no statistical tests were performed. Differences were noted when there was a difference of >/=5 percentage points between any estimates being compared. Overall, 75.2% of HCP reported receiving an influenza vaccination during the 2013-14 season, an increase of 11.7 percentage points compared with the 2010-11 season estimate, but similar to the 72.0% coverage estimate reported in 2012-13. With the exception of LTC settings, coverage for the 2013-14 season was higher in all work settings compared with the 2010-11 and 2011-12 seasons. However, overall, only HCP working in hospital settings had an increase in coverage during the 2013-14 season compared with the 2012-13 season. By occupation type, coverage during the 2013-14 season was 92.2% among physicians, 89.6% among nurse practitioners/physician assistants, 90.5% among nurses, 85.7% among pharmacists, 57.7% among assistants/aides, 87.4% among other clinical personnel, and 68.6% among nonclinical personnel. Only nurses and other clinical personnel had increased coverage compared with the 2012-13 season (90.5% versus 84.8% and 87.4% versus 81.9%, respectively). During the 2013-14 season, influenza vaccination coverage was higher for HCP working in settings where vaccination was required (97.8%) compared with HCP working in settings where vaccination was not required but promoted (72.4%) or settings where there was no requirement or promotion (47.9%). Influenza vaccination coverage was above 96% in all work settings where vaccination was required, including LTC settings. Thirty-six percent of HCP were required by their employer to be vaccinated, an increase from 13% during the 2010-11 season. HCP working in hospitals were more likely to be required to be vaccinated (58.2%) than those working in other settings (range = 20.1%-33.6%), whereas HCP working in LTC settings were least likely to be required to be vaccinated (20.1%). HCP working in LTC settings were most likely to report that their employer neither required nor promoted vaccination (42.6%) compared with HCP working in other health care settings. In contrast, only 7.0% of HCP working in hospitals reported that their employer neither required nor promoted vaccination. The majority of vaccinated HCP (77.3%) reported receiving the vaccination at work. Among HCP without an employer requirement for vaccination, vaccination coverage among HCP working in facilities that made vaccination available on-site at no cost for more than 1 day was 80.4%, compared with 61.6% in facilities that made vaccination available at no cost for 1 day only and 49.0% in facilities that did not provide influenza vaccination on-site or offered on-site vaccination but not at no cost. On-site vaccination for more than 1 day at no cost was more likely to be available to HCP working in hospitals (75.1%) than to HCP working in ambulatory care settings (43.0%), other clinical settings (31.1%), and LTC settings (14.6%). Among vaccinated HCP, the most common reasons given for vaccination were "To protect myself from flu" (43.5%), "My employer requires me to be vaccinated for flu" (25.5%), and "To protect patients from getting flu" (8.5%). Among unvaccinated HCP, the most common reasons given for not being vaccinated were "I might get sick from the vaccine" (20.1%), "I don't think that flu vaccines work" (16.3%), and "I don't need it" (16.0%).