Revenue

The following table summarizes our revenue recognized in our consolidated condensed statements of operations:



	Three Months Ended March 31,
	2019		2018
Net product revenue	$	4,692.3	$	4,605.9
Collaboration and other revenue ⁽¹⁾	399.9		357.9
Revenue	$	5,092.2	$	4,963.8

⁽¹⁾Collaboration and other revenue associated with prior period transfers of intellectual property was $35.5 million and $50.1 million during the three months ended March 31, 2019 and 2018, respectively.

We recognize revenue primarily from two different types of contracts, product sales to customers (net product revenue) and collaborations and other arrangements. Revenue recognized from collaborations and other arrangements will include our share of profits from the collaboration, as well as royalties and upfront and milestone payments we receive under these types of contracts. See Note 4 for additional information related to our collaborations and other arrangements. Collaboration and other revenue disclosed above includes the revenue from the Trajenta^® and Jardiance^® families of products resulting from our collaboration with Boehringer Ingelheim discussed in Note 4. Substantially all of the remainder of collaboration and other revenue is related to contracts accounted for as contracts with customers.

Disaggregation of Revenue

The following table summarizes revenue by product:



	Three Months Ended March 31,
	2019						2018
	United States (U.S.) ⁽¹⁾		Outside U.S.		Total		U.S. ⁽¹⁾		Outside U.S.		Total
Revenue—to unaffiliated customers:
Endocrinology:
Trulicity^®	$	665.6	$	214.1	$	879.7	$	528.2	$	150.1	$	678.3
Humalog^®	448.6		282.2		730.8		504.1		287.6		791.7
Forteo^®	125.9		187.0		312.9		122.1		191.1		313.2
Humulin^®	201.3		96.4		297.7		221.6		104.3		325.9
Basaglar^®	198.2		53.2		251.4		126.7		39.3		166.0
Jardiance	125.2		78.4		203.6		95.0		56.0		151.0
Trajenta	47.4		84.6		131.9		54.1		87.0		141.1
Other Endocrinology	61.7		60.3		122.1		64.1		67.5		131.5
Total Endocrinology	1,873.9		1,056.2		2,930.1		1,715.9		982.9		2,698.7

Oncology:
Alimta^®	281.8		217.4		499.2		245.3		254.3		499.6
Cyramza^®	75.1		123.2		198.3		68.3		115.3		183.6
Erbitux^®	113.3		5.1		118.4		121.3		28.3		149.6
Verzenio^®	93.5		15.9		109.4		29.7		—		29.7
Other Oncology	30.2		57.3		87.4		45.6		48.4		94.1
Total Oncology	593.9		418.9		1,012.7		510.2		446.3		956.6

Neuroscience:
Cymbalta^®	10.3		153.8		164.1		12.2		157.3		169.6
Zyprexa^®	9.3		97.9		107.2		8.8		113.8		122.6
Strattera^®	1.5		64.7		66.2		46.9		83.7		130.7
Emgality^®	12.2		2.1		14.2		—		—		—
Other Neuroscience	17.8		23.5		41.4		23.3		26.7		49.8
Total Neuroscience	51.1		342.0		393.1		91.2		381.5		472.7

Immunology:
Taltz^®	180.8		71.7		252.5		111.2		35.3		146.5
Other Immunology	6.4		75.7		82.2		—		32.2		32.2
Total Immunology	187.2		147.4		334.7		111.2		67.5		178.7

Other
Cialis^®	143.2		164.9		308.2		313.4		182.0		495.4
Other	41.5		72.0		113.4		53.7		108.0		161.7
Total Other	184.7		236.9		421.6		367.1		290.0		657.1
Revenue	$	2,890.8	$	2,201.4	$	5,092.2	$	2,795.6	$	2,168.2	$	4,963.8

Numbers may not add due to rounding.

⁽¹⁾U.S. revenue includes revenue in Puerto Rico.

The following table summarizes revenue by geographical area:



	Three Months Ended March 31,
	2019		2018
Revenue—to unaffiliated customers ⁽¹⁾:
United States ⁽²⁾	$	2,890.8	$	2,795.6
Europe	900.3		864.2
Japan	543.7		537.0
Other foreign countries	757.4		767.1
Revenue	$	5,092.2	$	4,963.8

Numbers may not add due to rounding.

⁽¹⁾Revenue is attributed to the countries based on the location of the customer.

⁽²⁾U.S. revenue includes revenue in Puerto Rico.

Adjustments to Revenue

Adjustments to revenue recognized as a result of changes in estimates for our most significant U.S. sales returns, rebates, and discounts liability balances during the three months ended March 31, 2019 and 2018 for products shipped in previous periods were approximately 3 percent of revenue and 4 percent of U.S. revenue, respectively.

Contract Liabilities

Our contract liabilities result from arrangements where we have received payment in advance of performance under the contract and do not include sales returns, rebates, and discounts. Changes in contract liabilities are generally due to either receipt of additional advance payments or our performance under the contract.

The following table summarizes contract liability balances:



	March 31, 2019		December 31, 2018
Contract liabilities	$	286.4	$	298.7

Revenue recognized from contract liabilities during the three months ended March 31, 2019 and 2018 was not material. Revenue expected to be recognized in the future from contract liabilities as the related performance obligations are satisfied is not expected to be material in any one year.