Web surveys present methodological challenges including lower response rates as compared to other survey methods. The literature on invitations to participate in web surveys builds on previous research suggesting that advance letters are cost-effective means for increasing response rates in mail surveys and interviewer-administered surveys. The efficacy and appropriateness of design elements of invitations to participate in a web survey is not yet well understood. This research reports results of a full-factorial experiment (n = 15,652) of five design elements of web survey invitations— invitation mode, subject line, location of URL link, length of the invitation text, and survey time/effort estimate. There were significant effects of different design elements on response rates. The results suggest that some design elements of invitations may have similar effects across subsets of populations, while others may have different effects on different subsets of potential respondents.