How can I get enough protein on a vegetarian diet?

Getting enough protein is not a problem if you are eating a varied diet and are getting enough calories to meet your energy needs. In fact, the only ways to guarantee a protein deficiency is to eat only those foods which fall below 10% protein on a per calorie basis (certain fruits and refined oils), or eat exclusively junk food.

For most westerners the problem is consuming far too much protein, which is linked to a number of diseases including osteoporosis, obesity, liver disease and kidney failure. Amino acids, the building blocks of protein, are found in all plants, and this includes the eight essential amino acids humans must obtain from food.

Those vegetarian foods highest in overall protein content include legumes or pulses (dried beans and peas), soy products of various kinds (tofu, tempeh, meat analogues), eggs and dairy  products for those who consume them, and some nuts (almonds contain 20% protein). While, at one time, some nutritionists thought it was important to eat complementary proteins at the same meal, more recent studies have shown that this practice is unnecessary.

Protein is found widely in plant foods and it is not difficult to meet protein needs from a plant based diet - most people eat more protein than they need.  Good sources include legumes, soy products (eg tofu, tempeh), nuts and seeds and some grains like quinoa and amaranth.  Eggs and dairy products also provide protein for those who eat them.

..Look, most individuals can source adequate protein from veg foods includine legumes frequenly in the diet. The challenge lies with very active vegetarians and especially vegans that require more than the standard aprox 0.8g/kg body weight protein. I find a protein drink useful in this area. adding to pea protein to rice milk or using a soy based meal replacement drink eg.Natural  PXR which is what I use, makes life a little easier. Those of you us/you with sensitive tummies also know that there is a limit to how much legume matter one can stomach in a day.

MS

It's easy for vegetarians & vegans to get complete protein from plants.  Just like everybody else vegetarians and vegans need complete protein to get all the essential amino acids, so their bodies don’t fall into a negative protein balance – otherwise known as starvation.  
Protein Requirements vary depending on  age, size, growth, health, physical activity, body type, pregnancy and lactation.
Protein is essential for health, along with carbohydrates and fats. We use amino acids as building blocks, to make protein, for every part of our bodies: blood, skin, cartilage, muscles and bones, hormones and enzymes.  Our bodies can synthesize 16 of the 23 amino acids that we need. That leaves 8 essential amino acids which must come from the foods we eat.
The Essential Amino Acids Have Important Functions In The Body:
Isoleucine (Ile) - for muscle production, maintenance and recovery after workout. Involved in hemoglobin formation, blood sugar levels, blood clot formation and energy.
Leucine (Leu) - growth hormone production, tissue production and repair, prevents muscle wasting, used in treating conditions such as Parkinson’s disease.
Lysine (Lys) - calcium absorption, bone development, nitrogen maintenance, tissue repair, hormone production, antibody production.
Methionine (Met) - fat emulsification, digestion, antioxidant (cancer prevention), arterial plaque prevention (heart health), and heavy metal removal.
Phenylalanine (Phe) - tyrosine synthesis and the neurochemicals dopamine and norepinephrine. Supports learning and memory, brain processes and mood elevation.
Threonine (Thr) monitors bodily proteins for maintaining or recycling processes.
Tryptophan (Trp) - niacin production, serotonin production, pain management, sleep and mood regulation.
Valine (Val) helps muscle production, recovery, energy, endurance; balances nitrogen levels; used in treatment of alcohol related brain damage.
Histidine (His) - the ‘growth amino’ essential for young children. Lack of histidine is associated with impaired speech and growth. Abundant in spirulina, seaweed, sesame, soy, rice and legumes.
Complete and Incomplete Protein:
ALL plant based foods have varying amounts of protein (plus carbohydrates, fats and other good things), and the body will combine proteins from all sources, to make ‘complete protein’. That's true for everybody, veg or non-veg.  The Term  'complete protein' means that all eight essential amino acids are present in the correct proportion.  Foods from animal sources have complete proteins . Some foods from the plant kingdom, such as soy and quinoa, have complete protein.  The term ‘incomplete protein’ refers to foods which have all the essential amino acids, but are low in one or more of them. That's called the 'limiting amino acid'.  Most plant foods have one or more limiting amino acids which limit the availability of all the other amino acids in the food. That's why these foods are called 'incomplete proteins'.  For example, the limiting amino acid in grains is usually lysine (Lys); in legumes it can be methionine (Met) and tryptophan (Trp). So, the low level of Lys in grains is complemented by a higher level in legumes, and vice versa, to make ‘complete protein’.
However, vegetarians and vegans don't need to worry about complete and incomplete protein. It is NOT NECESSARY for vegetarians and vegans to combine specific protein foods at one sitting to make complete protein. Vegetarians  need a healthy variety of good protein building foods, so the body can make enough complete proteins to be happy, even though you don't need to worry about how and when you combine them.
What Vegetarians Should Eat To Get Enough Protein:
Each plant food has its own unique amino acid profile, from green leafy veggies to tubers, from barley to quinoa, from lentils to tofu, from macadamias to brazil nuts. By eating a variety of plant foods with ‘incomplete proteins’ throughout the day, vegetarians can easily get enough ‘complete protein.’ For lacto and ovo-lacto vegetarians, any food can be complemented by the high quality proteins in dairy products or eggs, but it isn't at all necessary to include animal foods to get enough protein in your diet.  
Your body puts together amino acids from plant foods to give you complete protein throughout the day. For instance, the amino acids in beans & lentils are balanced by those in grains, nuts and seeds, and vice versa. Soy is a good source of protein and in the form of tofu is fine.
Vegetables and fruits also contribute significant amounts of protein. A one cup serving of avocado, for example, has 3 grams of protein, and a medium potato with skin has 4 grams.

The average person can get sufficient protein from plant foods.  A small amount of protein is found in grain foods such as breads and cereals.  It is also in nuts and other legumes and pulses such as lentils and chickpeas as well as tofu, tempeh and soy beans.  Dairy foods such as cheese, milks and yoghurts all contain protein as do eggs.  A well balanced, plant based diet can provide all the nutrition required for most people.