In 2003-2004 the flora and vegetation of Timber Island, the largest undeveloped island in Lake Winnipesaukee, New Hampshire, was studied. Utilizing both a vegetation analysis and floristic survey the island was found to have 190 vascular plant species. Abundance and frequency data were recorded from 106 plots and examined using a two-way indicator species analysis program (TWINSPAN). The result was the identification of six cover types, and two additional cover types were recognized through qualitative field observation. The flora of Timber Island was further analyzed in relation to three other known island floras in Lake Winnipesaukee: Rattlesnake Island, Bear Island, and Three Mile Island. Two indices of similarity, Sorensen's Index and the Simple Matching Index, were utilized to compare the floras. Similarities to Timber Island, based on Sorensen's Index were 49.7% for Bear Island, 51.2% for Rattlesnake Island, and 51.8% for Three Mile Island. Results from the Simple Matching Index showed higher levels of similarity: Rattlesnake Island 58.3%, Bear Island 63.4%, and Three Mile Island 53.9%. In addition to the vascular flora, ground cover, soil type, and bryophophyte diversity were studied. Fifteen new records of bryophytes for Belknap County were recorded. Further discussed are the topics of turnover rates, rare plant preservation under pressure from elevated deer populations, and insularity of freshwater islands. This work brings up conservation questions and in a time of accelerated climate change this serves as a solid base-line floristic record of the environment of Timber Island, and the greater Lake Winnipesaukee region. Finally the reader is invited to query different methods of conversation and to consider freshwater lakes and their islands within, as perhaps more dynamic to the local ecology than may have otherwise been assumed. Full flora, photographs, and an extensive list insular botanical works are included.