of higher hosting costs due to increased transaction volume as well as higher compensation costs associated with additional personnel to support growth in active locations. Professional Services and Other Total professional services and other cost of revenue increased $0.8 million, or 24.0%, to $4.0 million for the nine months ended September 30, 2021 from $3.2 million for the nine months ended September 30, 2020. This increase was primarily the result of increased consulting costs and higher compensation costs to support growth in active locations. Gross Profit Gross profit margin decreased to 79.5% for the nine months ended September 30, 2021 from 80.3% for the nine months ended September 30, 2020. Decreases in gross profit margin were driven by higher platform and professional services and other compensation costs to support rapid growth in transactions and active locations coming onto the platform. Operating Expenses Research and Development Nine Months Ended  September 30, Change 2021 2020 $ % (in thousands, except percentages) Research and development $ 42,872 $ 22,715 $ 20,157 88.7 % Percentage of total revenue 39.2 % 33.5 % Research and development expense increased $20.2 million, or 88.7%, to $42.9 million for the nine months ended September 30, 2021 from $22.7 million for the nine months ended September 30, 2020. This increase was primarily the result of higher compensation costs associated with additional personnel and an increase in the use of software tools to support further investments in our platform development and continued product innovation. Additionally, we incurred a non-cash charge of $1.8 million in March 2021 related to the vesting and settlement of SARs in connection with the IPO. As a percent of total revenue, research and development expenses increased to 39.2% for the nine months ended September 30, 2021 from 33.5% for the nine months ended September 30, 2020. General and Administrative Nine Months Ended  September 30, Change 2021 2020 $ % (in thousands, except percentages) General and administrative $ 53,034 $ 15,137 $ 37,897 250.4 % Percentage of total revenue 48.5 % 22.3 % General and administrative expense increased $37.9 million, or 250.4%, to $53.0 million for the nine months ended September 30, 2021 from $15.1 million for the nine months ended September 30, 2020. This increase was primarily a result of increased compensation costs due to increased headcount to support the growth and stage of the organization, IPO-related bonus awards, vesting and settlement of stock appreciation rights, or SARs, in connection with the IPO, as well as increased insurance costs and professional fees incurred in preparation for becoming and operating as a public company. Additionally, we incurred a non-cash charge of $13.1 million for the nine months ended September 30, 2021 related to the donation of 345,836 shares of our Class A common stock to a charitable donor-advised fund. We intend to donate additional shares to this fund in conjunction with our Olo for Good initiative. As a percent of total revenue, general and administrative expenses increased to 48.5% for the nine months ended September 30, 2021 from 22.3% for the nine months ended September 30, 2020. 37