The economic relationship between India and the United States is widely seen as good for both sides. Two-way trade is growing and, alone among Asian countries, India routinely trades more with the United States than it does with China, its neighbor and rival.

Yet under President Trump, trade is a point of friction. Like virtually all countries that do business with the United States, India runs a surplus: Last year it shipped about $87 billion worth of goods and imported $42 billion, adding $46 billion to America’s trade deficit.

Mr. Trump does not like those kinds of figures. He has railed against countries that sell more to the United States than they buy. Cue his furious imposition of tariffs on both allies and foes, provoking threats of retaliation and unsettling global commerce.

During his first term, President Trump called India “the tariff king.” He pointed to Indian duties as high as 100 percent on some American goods. He was particularly focused on a tariff he said was blocking Harley-Davidson from exporting more motorcycles. When India’s trade officials reduced that tariff, Mr. Trump paraphrased them: “ ‘We want to keep your president happy.’ Isn’t that nice?”

This week, when Mr. Trump sits down in Washington with Narendra Modi, India’s prime minister, tariffs are expected to be a topic of conversation again. Here’s what you need to know about the trading relationship between India and the United States.