Stock-based compensation expense for restricted stock, restricted stock units, stock options and issuances of common stock pursuant to our employee stock purchase plan was classified in the accompanying consolidated statements of operations as follows:



	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
	(in thousands)
Stock-based compensation expense:
Cost of revenue	$	718	$	469	$	1,291	$	843
Research and development	4,054		2,850		7,228		5,416
Sales and marketing	2,942		2,055		5,406		3,618
General and administrative	2,716		1,976		5,139		3,698
Total stock-based compensation expense	$	10,430	$	7,350	$	19,064	$	13,575

We recognize compensation cost of all awards on a straight-line basis over the applicable vesting period, which is generally four years.

Restricted stock and restricted stock unit activity during the six months ended June 30, 2019 was as follows:



	Restricted Stock				Restricted Stock Units
	Shares		Weighted-Average Grant Date Fair Value		Shares		Weighted-Average Grant Date Fair Value
Unvested balance as of December 31, 2018	21,677		$	10.88	2,773,773		$	21.21
Granted	—		—		1,509,033		41.83
Vested	(21,677	)	10.88		(594,764	)	22.88
Forfeited	—		—		(174,261	)	25.31
Unvested balance as of June 30, 2019	—		$	—	3,513,781		$	29.58

As of June 30, 2019, the unrecognized compensation expense related to our unvested restricted stock units expected to vest was $97.1 million. This unrecognized compensation expense will be recognized over an estimated weighted-average amortization period of 2.8 years.



	Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2018	3,713,179		$	10.32
Granted	—		—
Exercised	(549,612	)	11.02			$	21,286
Forfeited/cancelled	(26,013	)	12.88
Outstanding as of June 30, 2019	3,137,554		$	10.17	5.7	$	149,561
Vested and exercisable as of June 30, 2019	2,416,849		$	8.90	5.1	$	118,275

As of June 30, 2019, the unrecognized compensation expense related to our unvested stock options expected to vest was $4.5 million. This unrecognized compensation expense will be recognized over an estimated weighted-average amortization period of 1.5 years.

The total fair value of stock options vested in the six months ended June 30, 2019 was $3.8 million.

Under the Rapid7, Inc. 2015 Employee Stock Purchase Plan (ESPP), employees may set aside up to 15% of their gross earnings, on an after-tax basis, to purchase our common stock at a discounted price, which is calculated at 85% of the lesser of: (i) the market value of our common stock at the beginning of each offering period and (ii) the market value of our common stock on the applicable purchase date.

On March 15, 2018, we issued 123,607 shares of common stock to employees for aggregate proceeds of $1.6 million. The purchase prices of the shares were $12.96 and $14.78 per share, which were discounted in accordance with the terms of the ESPP from the closing prices of our common stock on March 16, 2017 of $15.25 and on September 18, 2017 of $17.39, respectively.

On September 14, 2018, we issued 96,108 shares of common stock to employees for aggregate proceeds of $2.0 million. The purchase prices of the shares were $21.96 and $14.78 per share, which were discounted in accordance with the terms of the ESPP from the closing prices of our common stock on March 16, 2018 of $25.84 and on September 18, 2017 of $17.39, respectively.

On March 15, 2019, we issued 110,822 shares of common stock to employees for aggregate proceeds of $2.6 million. The purchase prices of the shares were $30.46 and $21.96 per share, which were discounted in accordance with the terms of the ESPP from the closing prices of our common stock on September 17, 2018 of $35.84 and on March 16, 2018 of $25.84, respectively.