If you're single and considering adoption, you may have already been warned of the prejudices against single adoptive parents. Singles are certainly nontraditional adopters, but there's nothing keeping a single person from adopting. However, that doesn't mean most agencies will either turn you away or try to place a special needs child with a single adopter. Nontraditional adopters are more likely to be matched with a child that is difficult to place with traditional adopters.
The biggest obstacle that single parent adopters will face are the objections to single parents during the adoption process. Many single biological parents successfully raise children, therefore many single adoptive parents can as well. But single adopters are set back by the stereotype that most single parents are struggling workaholics. While this isn't true for every adoptive single parent, it may explain why many pregnant women seeking placement are less likely to place with a single parent.
It's not impossible to adopt as a single person. Singles can expect upfront rejection from some agencies and singles may only be considered for special needs children that are not being placed elsewhere. Singles have better placement chances via international adoption. Every country has unique single parent adoption requirements. In China, a male adopter has to be 40 years a female adoptee's elder before he'll be considered for placement.
Singles have every right to adopt and raise a child, but it's the unfortunate truth that you'll likely need to be prepared to articulate a strong argument or responses to objections that a case worker may present.