A ladder is a vertical or inclined set of rungs or steps commonly used for climbing or descending. There are two types: rigid ladders that are self-supporting or that may be leaned against a vertical surface such as a wall, and rollable ladders, such as those made of rope or aluminium, that may be hung from the top. The vertical members of a rigid ladder are called stringers or rails (US) or stiles (UK). Rigid ladders are usually portable, but some types are permanently fixed to a structure, building, or equipment. They are commonly made of metal, wood, or fiberglass, but they have been known to be made of tough plastic.

सीढ़ी या सोपान एक यांत्रिक औजार है जो धरातल से उपर चढ़ने या नीचे उतरने के काम आती है। इसमें उर्ध्वाधर या झुके हुए बहुत से 'चरण' होते हैं। सीढ़ी मुख्यत: दो प्रकार की होती है -

• लकड़ी, लोहा, एलुमिनियम आदि की अचर (रिजिड) सीढ़ी, तथा
• रस्सी की सीढ़ी जो किसी आश्रय से लटकाई जाती है।